I think there might be too many intervening factors to answer your question in satisfactorily. You're asking competitive smashers about how they adjusted to two minute time matches with items, in addition to new control schemes, new game physics, new characters, and a new new final smash ball mechanic? What qualifies as having adjusted?
The new physics in general don't take too long to learn since the game is slower and floatier. On the otherhand, I avoided the ground in general because I feel inept there without without wavedashing. Another sore point for me was how characters now die around 150 percent instead of 100. I kept focusing on killing them around 100 and it of course didn't work.
My characters ICs and puff weren't playable so I decided to try new characters, primarily sonic but also metaknight. Of course, I wasn't nearly as good with them as my melee mains, and I presume it will take many hours of practice to become as good.
Items weren't too tough to adjust to but they are can be incredibly annoying. Some pretty much guarantee that your going to own for 20 seconds. Hammers, Mario Kart lightning, spicy chili ... Its annoying to drop everything and pick those up because you don't want your opponent to.
I hope this helped