Surely some will tell me that it is scientifically proved that BL is garbage and Warband is great, I'm curious.
Compare them on the fundamental feature they share which they did not try to reformulate from one to the next: combat. It's still four directions for attacking and blocking, four weapon/shield slots, feints, kicks, and chamber blocks. New mechanics are really just variations on existing mechanics or techniques: directional shield blocking is just more forgiving weapon blocking, shield bashes and hilt strikes are just lighter kicks which don't root you in place, combos are just double swings with bespoke animations, block crushing was expanded beyond two-handed maces to include other two-handed weapons. Stances were a mechanic that did alter the combat system in new ways, but I believe that was tuned down to the point where it's purely visual. So, not really a lot of innovation on this front overall and honestly that should be a
good thing because M&B's combat is what sets it apart from all imitators. Readable and responsive, not too twitchy, and with lots of space to play mind games. The whole experience was tight, with all the pieces sized & fit properly.
Unfortunately, while Bannerlord is still well ahead of many other games which have tried to recreate that magic, it's not as readable or responsive as Warband was. Bannerlord looks nicer in general, though some of the animations are still a bit awkward (nature of the beast for the 4-direction system we have, so it's forgivable), yet because the animations aren't as exaggerated as Warband's it is a tad more difficult to read them. For your standard 4 attack directions it's no big deal, but the combo system's chained attack animations can be misleading. For instance, chained one-handed left swings are pulled back to the right, then pass over and behind the attacker's head before coming back out on their left. In terms of responsiveness it has certainly improved a ton since the stance modifiers were taken out. Blocking and attacking on the "wrong" side from your stance were incredibly slow. Still, it doesn't feel as crisp as Warband did. Shield blocking for the longest time had a readability/responsiveness problem as the defender, where weapons which did not physically collide with the shield model would not be blocked by it, which resulted in being struck in the head over your shield or from the sides while actively blocking. I bet that's still in there to some degree but I haven't really noticed it since launch, because I believe some of the shield "forcefield" is back for melee now. I could be wrong, because I've been running lots of two-handers (crush-through is broken, more on that in a bit).
The other most noticeable changes to combat were tolerance-based. In Warband, a chamber block was executed by (roughly) facing your opponent and beginning an attack of your own on the same side that an enemy attack was about to hit you from. If your enemy was swinging on their left (your right) then you would begin a right swing within a short window to block that attack while readying your own. Fundamentally this remains the case in Bannerlord, but in terms of execution the window is much narrower and the leniency in your facing is incredibly small. It is my understanding that your weapon model must actually collide with the incoming weapon model for the mechanic to function, which makes it remarkably more difficult to accomplish for some attack directions when compared to others. This inconsistency discourages people from learning the mechanic, especially with how disproportionate the risk is compared to the reward. The second major tolerance-based change is the crush-through on two-handed weapons, which nobody seemed to really want and which many people have complained about. The mechanic gave two-handed maces a niche in Warband, but having the mechanic available to all two-handers in Bannerlord makes it less interesting and more annoying. Success is based on speed bonus and weight, as far as I know, and it's compared against the defender's weapon's weight when they block. Some two-handed weapons will consistently crush through pretty much all one-handed weapons, and in SP at least it is commonplace for two identical two-handed weapons to crush through each other regularly. Battanian tournaments can be quite a nuisance when it comes down to dueling with two-handed axes.
Is Bannerlord garbage in this compared to Warband? No, I don't think so, but it's like going from name-brand tortilla chips to store-brand. It's still cut tortillas fried and salted, it's still the best thing available to go with your salsa, but they're a little greasier and not as crunchy. Thankfully it's a lot easier to make your own tortilla chips than to make your own M&B.