Not discussing whether it's against ToS but the morality of creating new accounts purposely to "speed run", i.e. see how fast you can get the rating up.
On
chess.com I have seen them do this but the account is marked in a way such that any rating points lost to it are refunded, i.e. whilst this account will gain rating points when they win, the one they beat won't lose any if they lose. So a 2200 player (or higher) can create an account with an 800 start rating (I think I saw someone start with 400) then play a lot of blitz or bullet to see how quickly they can get that rating up.
Despite the rating points refund, I'm not sure 1000 rated players want to be playing against 2200 rated players with a much lower rating because they come to play what they hope will be a fair game of chess, against a player displaying a rating that matches their ability. That is why sandbagging is immoral and banned on this site.
However, I have seen a user with 2 accounts who uses one account only for arenas where they berserk every game (and when I watched them, they also played a technically inferior opening, albeit without an exchange sacrifice). In theory, that makes their rapid rating probably lower than it would be if they played normally, but it is not immoral as such as they play the same against everyone. In fact it's probably more moral, as when they are not playing in an arena and thus not berserking (and possibly playing a normal opening) their rating is higher which reflects their real skill ability. So for this purpose, I actually think having a separate account is commendable.