I do not want to sound like a Bannerlord fanboy but for people saying that Warband SP is currently better, can you please elaborate why vanilla Warband SP is better? Bannerlord, even when It stills need new features a lot of polishing, even when Diplomacy and AI Lords relationship is almost inexistant, I find It much more enjoyable than Warband and It has new great features that Warband does not have.
Vanilla Bannerlord is already superior than vanilla Warband in SP for me without any doubt.
Here's my reasons, for what is worth, listed in order of annoyance (biggest gripe comes first):
1) While it is not optimal, in Warband having an infantry army is perfectly feasible and enjoyable, and if cavalry charges blindly against a blob of Rhodok Sergeants or Nord Huscarls, they are going to have a bad time. In Bannerlord cavalry will just gracefully slide through small gaps as if they were made of rubber. It's immersion breaking and unfun, not to mention unbalanced.
2) There is no training skill in Bannerlord (Leadership perks are largely irrelevant), so you have to gather low level recruits and send them to fight while you semi-afk from your high horse. I don't consider this a fun activity.
3) Low level archers in Warband will tickle you if you have decent armor, while high level archers will hurt a lot. In Bannerlord there is much less of a difference in skill between low and high level archers, which removes a level of depth to the game.
4) In Warband you have complete control over the way you level, while in Bannerlord you really have no control over what skills you raise.
I am hoping that a lot of this will be addressed during development, but as for right now yeah that would be why.