Nope. Sandbox means just what it means. I bet you believe Skyrim was a sandbox because you didnt "have to" do quests. By your definition, World of Warcraft was a sandbox just because it was open world...lol. No. Wurm Online and Eve were 2 of the extremely few actual sandbox MMOs and M&B IS one of the few actual sandbox games there are. Total War is that way ----->
... You should interact with lords more, and their relationships with you and their personalities should matter...
I agree with you on your priority. Combat, AI and tactics are by far the number one things to improve. But that doesn't contradict the demand for RPG elements. RPG does not mean boring grind, it just means depth, immersion and possibilities to play as you please as a player. And in that regards M&B was always an RPG. If you don't like a living world to immerse yourself in then you don't have to - as long as the unique M&B core works.
What do will players do if there is no RPG mechanics? 99% repetitive fighting and 1% of kingdom management? Game will be even more desolate without RPG stuff.