Starting with 1, Your character still can't be good at things you don't train for. One game I made a Xbow user. Next I made a sword guy. You get bored of the playthrough eventually, map is already mostly painted or going to be, or you just want to write a different story. It's not like your guy can pick up a weapon they've never used and dominate with it. Considering that the rest of the group who specializes will be able to fight way harder guys than the dude who tried to be a martial artist - xbow user. But, the martial artist - xbow user can run really fast and dodge well, so there is a class unto itself, not as good at shooting as pure xbow, or at fighting as martial artist, but good enough at shooting to be ok and able to keep alive long enough for help to arrive.
What you're looking for in variety is better served by more meaningful alternatives to being a mercenary/slaver/farm pillager/venture capitalist until you become king. What if they fleshed out banditry and there were legitimate reasons to use throwing weapons and have a bad reputation, that this could be another path to being king and ruling through fear instead of honor. Or maybe you can 'redeem' yourself in the eyes of the people and turn your life around depending on what you do. That would be really interesting for reasons that have nothing to do with focus point allocations.
Making it so because you are good at managing a settlement and fighting you can't also be good at running an army too because running an army and running a settlement use different stat points but for some unknown reason you can be a good medic is a fairly obtuse way to force 'unique' characters.
Actual gameplay variety is the order of the day to get what you desire here, and there are much better ways than simple character stats.
2 Technically Kenshi is a large scale warfare game in many of the same ways that M&B is. Battles can easily feature a similar number of onscreen combatants as in Warband in some areas. Both games have rudimentary strategy in terms of positioning and attack orders, but nothing to the level of a tactical wargame or a CRPG. So I make a very fair comparison. Especially considering you can have any number of 'castles' and villages that you can build and defend against sieges while destroying other factions. Its a lot more similar than you think. We certainly seen a lot of Warband refugees hungry for something similar while waiting for Bannerlord on reddit when Kenshi came out. They all made the same comparison - not exactly the same but quite similar feeling of starting a nobody and becoming whatever you want if you work for it. The interface is certainly different, and Kenshi is just giving orders not action like M&B, but very similar in a lot of ways.
Also consider that you get actual quests in Bannerlord. With actual dungeons no less! - bandit lairs - that you clear for loot(!). That's pretty 'open world' and 'adventure' to me. Hell, M&B has a lot more in common with most adventure style games than you're letting on.
3 The softcap is more of a way to make reaching 100 a challenging quest in itself. You'll have to capture at least 1 of the strongest boss type characters in the game and fight them arena style. It's not undoable, but it's not something that you're like 'OK, gotta go get the hardest guy and fight him for skillups before I leave the beginning area.' Type of thing. Think of it this way, if you conquered essentially all of Calradia, the last challenge you might decide is to reach level 63. So you might keep a kingdom alive just to farm xp till you get there. Not something that will define the playthrough, but something to do before you reroll. If you're into that sort of thing. I don't see how the softcap in WB enraged anybody, I don't think that's a very fair point.
One final point, addressing your changing classes on the battlefield, that is actually kinda realistic. To some extent. Depending on how liberal your interpretation. In medieval Japan samurai would first dual with bows, then fight with spear and sword. So they change from archer to spearman with backup sword. They were also the ruling class who were able horsemen that practiced horse archery. So very high level archery, spear, sword, horse riding and settlement management. Oh, and many of them were talented poets on top of it all. That this is impossible in Bannerlord is very unrealistic, at the very least. Certainly very disappointing that it isn't even an achievable long term goal like ruling the world.
Because it being easier to literally conquer the world than be good at leading an army, fighting in close quarters, engaging in archery and managing your community even though people did those very things in real life and it was no more or less uncommon than talented university students. That's good gameplay?
Actually you can pretty much pick up any weapon and wouldn't notice a bit of difference no matter what your skill is. Most enemies you'd one shot, you'll still one shot, most you'd two shot, you'll still two shot... you might save one swing every 10-15 kills but there really isn't much difference.