Eh, GT:S deviated away from what GT is supposed to be. It doesn’t mean that they couldn’t release a solely multiplayer project and have it succeed.
On the question of need - no, they don’t.
I mean....it's not bad (it's pretty decent) but just inferior compared to the mainline entries this pales in comparison (imo of course).
Bet with Intrinsic:
The Switch will outsell 3DS (based on VGchartz numbers), according to me, while Intrinsic thinks the opposite will hold true. One month avatar control for the loser's avatar.