Unraised levies are added to the garrison in a siege, so it's not like they are not helping.
The system was designed and works very well. There are however two flaws I've been able to found playing in Iberia (based on demo).
Example 1 :
- The duke of Portucale(1 province in demense +3 OPM counts hates his liege, King of Galicia (2 provinces demense) so he doesn't provide much levy.
- Castille calls it's ally Galicia to war on eastern side of Iberia.
- Emirate of Bandajoz declares holy war for Portucale. Invading it. King of Galicia immidiately returns home(the ai is actualy smart gj PI), but his allies are occupied and won't help him.
- Weakened Galician army can't beat the muslims so the war is lost.
- Whole Portucale is conquered and all portugese landowners are exiled. Galicia is reduced to 2PM
Now the portugese duke, his counts and their mayors + bishops could together munster an army that woud totaly kick muslim asses. However they don't. And since the game allows you to beat 600 garrison with 610 army without a scratch(not counting events), the levy added to garrison doesn't realy count much. So because they dispise their liege they get themselves owned. Weird isn't it?
Solution: Give a vassal(including barons), who is in danger of loosing land in war, massive temporary bonus to relations. Only usable in defense, so hardly exploitable.
Example: 2
-After a while I became the duke of Portucale and gained my independence on Galicia. The evil emirate of Bandajoz meanwhile got owned by Leon. However due to some weirdness they only lost 1 province to catholics and the rest (8 provinces total) became vassal of Leon under muslim rule.
-Now the emir, his counts and other emirate of Sevilla constatly dows me, using well prepared armies containing these pesky muslim horse mercs (again briliant ai). They are realy working in turns, so I beat one and other one dows etc.
-Since I have 4 provinces in demense and decent income I can defend myself, but at great cost.
The problem is I can't do anything to fight back. If I beat them they loose some prestige and piety,but that has very specific usage so they don't care at all. I can't invade, since I am constantly at war. But even if I could no cb vs muslims in Leon + it would be suicide(powerful allies all bigger then me). Conquering Seville wouldn't help either(unconnected wrong religion provinces and more muslims enemies).
My example is extreme, but basicaly any vassal can attack without much external danger. Playing Bohemia? You can attack Poland with ease, if you loose no big deal.
Solution: Loosing offensive war should hurt MUCH more than it does now and heathen vassals shouldn't get holy war cb.