I am 10+ hours into a playthrough and yet to see a single companion ever level. Sure, they still gain skills but not levels (and stats/focus points). This makes gear as the only path to upgrading your companions. Also, I have not encountered any merchant or stewardship companions. I expect assigning stewardship-focused companion to govern should increase bonuses to holdings. Likewise with Vay Tiền Nhanh Chỉ Cần Cmnd Nợ Xấu.

mount and blade 2 best companions