I max out all laws, whenever I can.
I think this is the main area where we differ. IMO, not all laws should be maximised. My usual desired endgame point is kingdom (not duchy) viceroys, mediumish centralisation and absolute council authority. I usually don't max out obligations either, but I think that's mainly because it's my lowest priority and I've usually broken the game by the time I get around to it. (Insert obligatory shoutout for more Crusade-style character-switching mechanics.)
Before getting to the Imperial Administration, it's hard to manage a large empire with just 15 vassals (that I'd have with completely restricted council), especially if they have gavelkind succession.
I'm not using Gavelkind, so my demesne size is 10 or 11 (depending on the ruler). Planning to expand it to 12 or 13. But I usually don't max it out, because my different rulers have different stewardship and different spouses. I can beat any viceroy and any duke with just my retinue alone. I can beat even all of them combined with my personal troops (levy included), and, if I couldn't, I'd just hire mercenaries.
I'm not relying on my levy, so vassal limit is more important to me than demesne size. I use my levy only to fight off raiders, if my retinues are far away, or for GHW, if there are too many enemy participants. Otherwise, I use only my retinues and my vasalized holy order.
Short story: quality over quantity.
Yes, that's a good policy. With high tech in your capital, good choice of retinue and high martial skill commanders, your retinues can wipe the floor with normal armies twice their size. More if the enemies are low-quality light infantry.
I think our main difference is that you want to max out centralisation asap, whereas I am willing to stick at low-medium until after I get Imperial admin. So, your early-game plan is to keep vassal limit high via council laws, whereas mine is to go absolutist and keep vassal limit high via lowish centralisation. At that level, the two strategies seem similar. However, there are other impacts - most notably, that you have to deal with constant council interference and that I can't change laws as often (10y instead of 5y). As you say, there are multiple ways to play the game - I like my way and you like yours
---
But, back on-topic: Another very good reason to get Conclave is the favour system. This enables you to pull in the best unlanded courtiers in the world, to act as your council and commanders. So you can have a high-stat Jewish chancellor, steward and spymaster for all of the sweet free techpoints. And you can also pull in commanders of other religions who have rare but extraordinarily-useful traits (eg. winter, siege).