The new system is a big step up from the old event troops, however I think it is heavily over-tuned at the moment and makes tribes more powerful than they should be relative to other government forms.
The Problem
The main issue is that it's too easy to get more retinue cap. The bulk of your capacity comes from the first fort building, giving 100 cap for only 37 gold. Since tribes get extra demesne size, it is quite easy to get your hands on a few tribal holdings, put lv 1 forts in them, and raise a substantial retinue army out of that. Even if those tribes are later lost due to gavelkind succession, you don't lose the retinues that you previously created. This makes it very easy to press claims on lost land or simply continue conquering territory with your old retinues. As long as the army is not completely wiped out, you just need to wait for it to replenish.
On top of this is the bonuses from technology and religion. The first level of military organization in your capital increases all of those retinue numbers by 2.5 times. If you're playing as a Germanic, this cap is further multiplied by 1.5. That totals to 3.75 times, giving 375 retinue cap for each lv 1 fort in Germanic tribes. The lv 1 weapon smith gives 25, which becomes 94. The level 1 market building gives 20, which becomes 75. That's a total of 544 for just the first level tribal buildings in one tribe, costing 100 prestige and ~75 gold to build. Many tribes start with some of these buildings.
Loading up as Sjaelland at the Old Gods start has him with 555 retinue cap without any lv 1 forts built in his three tribes. Adding those on gives him a total of 1680 retinue cap with only three personally held tribes, while he has a demesne size of 7. Using just the most basic tribal retinue, he could raise 2400 light infantry for 400 prestige with that, doubling his levy size. That can be used to raid for a lot more money and prestige, letting him get more tribes and even higher retinue cap. The forts are really cheep after all and he only needs the first level of them. If he also focuses military tech with the scholarship focus and picks up lv 2 military organization, that raises the retinue cap to 2688, enough for 3750 light infantry. Again, this is only three tribes out of seven demesne size.
I think this is where the main problem comes from. Tribes just get too much retinue cap too quickly and succession doesn't even take away the armies they make with retinues. So their military power is much higher than the settled governments.
Suggestions
This will probably take a few iterations to get the right balance. Tribes are really tricky to get right because of all the different bonuses they get from empty holdings and pagan religions and because they can use the entirety of their vassal's armies in wars. They probably should get some frontloaded retinue size, but it shouldn't be able to be spammed for such large results. Especially if the player rushes out military organization.
My initial idea is that the tribal government itself should give some of the frontloaded retinue size, to make sure they can make at least basic retinues without buildings. +100 retinue size from the tribal government should be good. This means everyone benefits from what the lv 1 fort gives, but they can't get multiple copies of it. Higher level fort and market buildings can still give some extra retinue size, but this comes online much later and costs a lot more to get to. Say +30 from level 3 and level 4 forts, while level 3 and 4 markets give +20, which totals up to 100 when fully upgraded.
It would probably also be a good idea to tone down the +50% bonus that Germanics get to retinue size, since that is applied multiplicative with the technology modifier. Alternatively make it additive with technology, so a 250% retinue size becomes 300% as a Germanic, rather than 375%.
Another look at the base tribal levies might also be in order, given how much larger their regular forces are now with all these retinues added on top of them. Perhaps empty holdings shouldn't add +50% to the troop and income anymore? It might be a good idea to bring that number down and maybe raise the base troop count a little bit so that provinces with 4-6 empty holdings aren't quite so incredibly powerful anymore, while those with none aren't quite so bad. It would also further shift more of the tribe's power into their retinues, which are easier to balance.
The Problem
The main issue is that it's too easy to get more retinue cap. The bulk of your capacity comes from the first fort building, giving 100 cap for only 37 gold. Since tribes get extra demesne size, it is quite easy to get your hands on a few tribal holdings, put lv 1 forts in them, and raise a substantial retinue army out of that. Even if those tribes are later lost due to gavelkind succession, you don't lose the retinues that you previously created. This makes it very easy to press claims on lost land or simply continue conquering territory with your old retinues. As long as the army is not completely wiped out, you just need to wait for it to replenish.
On top of this is the bonuses from technology and religion. The first level of military organization in your capital increases all of those retinue numbers by 2.5 times. If you're playing as a Germanic, this cap is further multiplied by 1.5. That totals to 3.75 times, giving 375 retinue cap for each lv 1 fort in Germanic tribes. The lv 1 weapon smith gives 25, which becomes 94. The level 1 market building gives 20, which becomes 75. That's a total of 544 for just the first level tribal buildings in one tribe, costing 100 prestige and ~75 gold to build. Many tribes start with some of these buildings.
Loading up as Sjaelland at the Old Gods start has him with 555 retinue cap without any lv 1 forts built in his three tribes. Adding those on gives him a total of 1680 retinue cap with only three personally held tribes, while he has a demesne size of 7. Using just the most basic tribal retinue, he could raise 2400 light infantry for 400 prestige with that, doubling his levy size. That can be used to raid for a lot more money and prestige, letting him get more tribes and even higher retinue cap. The forts are really cheep after all and he only needs the first level of them. If he also focuses military tech with the scholarship focus and picks up lv 2 military organization, that raises the retinue cap to 2688, enough for 3750 light infantry. Again, this is only three tribes out of seven demesne size.
I think this is where the main problem comes from. Tribes just get too much retinue cap too quickly and succession doesn't even take away the armies they make with retinues. So their military power is much higher than the settled governments.
Suggestions
This will probably take a few iterations to get the right balance. Tribes are really tricky to get right because of all the different bonuses they get from empty holdings and pagan religions and because they can use the entirety of their vassal's armies in wars. They probably should get some frontloaded retinue size, but it shouldn't be able to be spammed for such large results. Especially if the player rushes out military organization.
My initial idea is that the tribal government itself should give some of the frontloaded retinue size, to make sure they can make at least basic retinues without buildings. +100 retinue size from the tribal government should be good. This means everyone benefits from what the lv 1 fort gives, but they can't get multiple copies of it. Higher level fort and market buildings can still give some extra retinue size, but this comes online much later and costs a lot more to get to. Say +30 from level 3 and level 4 forts, while level 3 and 4 markets give +20, which totals up to 100 when fully upgraded.
It would probably also be a good idea to tone down the +50% bonus that Germanics get to retinue size, since that is applied multiplicative with the technology modifier. Alternatively make it additive with technology, so a 250% retinue size becomes 300% as a Germanic, rather than 375%.
Another look at the base tribal levies might also be in order, given how much larger their regular forces are now with all these retinues added on top of them. Perhaps empty holdings shouldn't add +50% to the troop and income anymore? It might be a good idea to bring that number down and maybe raise the base troop count a little bit so that provinces with 4-6 empty holdings aren't quite so incredibly powerful anymore, while those with none aren't quite so bad. It would also further shift more of the tribe's power into their retinues, which are easier to balance.
