Funny, in my opinion they're the best fights the game has to offer. The slow tide of battle with shifting flanks, sending polearm-users to and fro protecting vulnerable areas, pinning down advancing troops, etc. They're as tactical as BB gets, and offer something different from the regular brawls, while retaining all the benefits of brigand fights. They do drag on, of course, but they haven't been too common in my runs, maybe 3-4 per war (of which I've only had 2 in total). The loot you get is great, but I would enjoy the noble war fights even if it weren't.
They do drag on, a 20/30 soldiers on each side fight can wear you off and make you quit the game for a couple of days but i agree, they're quite interesting.
The next challenge being protecting your allies and getting no losses and fewer losses as possible for your ally.
Most would agree to say their billmen and pikemen are quite dangerous but i try to rush 2H swordmen before they can get in position and strike (which is usually not that hard, they're swamped by their own troops and can't strike before long) and you don't want to end up in close combat with a knight and his goons either.
A Fencer can help a lot to route them fast mowwing down their crossbowmen and billmen.
Legend Mod in Legendary difficulty wise, i took my save back, spent 2 perks points i was saving, got the lone berserker to lvl 7 and it finally turned alright, looks like i only had shitty rolls for the first 2 weeks or so.
Then i added a +6 roster upgrade after a couple more of level up and recruited (i overlooked theearly +2, +3 and +4 roster upgrades), it's now business as usual.
Still, all the brigands have the nimble perk (didn't notice at first) so do the webnecht and the Unholds now regen like 30-40% HP a turn instead or 10-15% ...
Also, Wielderganger now poison you and unlike the goblins poison, it doesn't wear off and increase in power, leaving you with 3AP after a couple of turns ...