Agree with everything you say and, if they want this game to work as a service driven title rather than having G versions, which I'm also 95% certain they'll be doing (Street Fighter style seasons supplemented by the standard MH free DLC support) then having two product lines makes even less sense.
Then continue with spin offs like Stories, Frontier etc.
I don't see anything about Monster Hunter World, save for it not having local co-op, that would make it feel out of place on a portable system. Adding local co-op to the game (as far as I can see) wouldn't necessitate any major design overhauls. In fact, the drop in/drop out multiplayer may actually suit local co-op extremely well.
See I completely agree with the way the drop in and out stuff is would fit the handheld co-op stuff easy. Now if Capcom even does that who knows.