Of course you can play in another role you made up - but the game's designers simply didn't put much effort into supporting such roles with full featured sets like they did for the commander role. So your experience would be limited BY DESIGN.
This is actually spot on.
I think Bannerlord is an okay/good combat sim.
Most* of the complaints (my comments included) are rooted in higher expectations. The superproductive ( ) "could have been much more" school of thought.
*not all, for example melee cavalry combat swing aim