Oh I somewhat disagree then.
A better-designed version of 5E could have that be fully true.
But unfortunately 5E and 1D&D aren't designed that way, and you have a lot of abilities based on specific class levels (like getting multiple attacks, and how spell progression works), such that if you MC a lot, you can easily end up drastically less powerful than other PCs, and if you multiclass extremely carefully and only with specific, compatible classes, you can be somewhat more powerful than other PCs. The former is a bigger mechanical issue than the latter, for sure.
Either way, there's virtually nothing genuine to be gained from MC'ing in 5E/1D&D, imho, for the game/group holistically, anyway.