This seems like an intelligent plan to port a high-end game.
1. From all of the reports including DF, this is a solid game that plays very well. I really doubt the avg gamer will notice or care about graphical differences considering the portable 720p screen. Docked maybe. Either way, if it wasn't a meh game that my son bought on XB1, I would likely consider.
2. Every game you buy now on any other console requires an install and sometimes patch. The fact that this is only required for multiplayer is a perfect trade-off to lower the cost on the cart. You can start playing the game immediately after inserting the cart (unlike any XB1/PS4 game) and while you play the multiplayer can download in background, if you want to even play it that way.
I sincerely hope that most big 3rd party games follow similar patterns. Game creation software is highly scalable as this game demonstrates. Can't wait to see what comes in 2018 as these companies tweak the engines a bit more after the initial work to support Switch.