I do think Bannerlord's leveling is too grindy, but the solution in my opinion would be to add more ways, active and passive, for companions and players to earn XP. Books and Scholars, training events, self-study and apprenticeship between members of the party, all of that would make leveling a much more pleasant experience. Currently leveling companions is so difficult that even with boosted XP gain through mods I still won't play with death enabled, for the simple reason that raising another expert follower would take me a whole game.