Agreed.
So, you had a bad gaming session in Bannerlord ... and something really annoying and frustrating happened. Yeah well - welcome to early access Bannerlord!
There are SO many fundamental things in this game that need fixing. This needs a few tweaks and adjustments... but it's not major. Not in comparison to so many other Bannerlord problems.
I disagree, I don't think this system can be tweaked into being good. I think in a game where the main gameplay feature is the combat, having a war suddenly get ripped from under you is the worst feeling ever. It takes a while to get invested in them, and even though they're grindy as hell, you want there to be a satisfying conclusion where you remove all their fighting capability for a while. Having the AI decide that on a whim whether to stop all the player momentum is counter to the entire premise of the game.
It's different in something like EU4 because you play as the country and aren't forced to be part of an alliance, but in Bannerlord you have no choice.