Incorrect. The rightside advancing mushroom mechanic was a deliberate game design choice all the way from the very first SMB and now a long time classic behaviour, it does not originate from NSMB DS and it may arguably be fine as-is even in the context of MvL, as even a slight bit of planning makes it really easy to grab one, meaning that players can get safe from death easier, allowing them to then focus more on fighting for stars, chasing players down, promoting a more active playstyle, thus doing anything but slowing down the gameplay.
Oviously that means that players won't die as frequently compared to a modified alternative where powerups are more challenging to get, but i think it has already been stated many times in the past that deathmatch is not the core gameplay of the original MvL nor of this remake, as both games are focused around hoarding and stealing stars.