The argument that "if you think it's OP, don't use it" rings hollow, especially in SMP. It's simplistic to declare the balance issue moot because someone who thinks a Powersuit is overpowered can choose not to use it... while everyone else on the server is flying around like Superman. To say that is to deny the competitive nature of gaming.
Your argument is based entirely on the incorrect assumption that everybody wants to be a sheep/lemming. (lemon for those who get the reference)
Using your argument above, you assume that every player wants to be able to fly.
I have no interest in flying in minecraft (or RL as a matter of fact), it just doesn't interest me in the game.
Back when I used IC I made the jetpack, because the guides said to do this and this and this, but I never felt the need or desire to use it. Sure when I was out wandering the wilderness for resources and came across a mountain I would use it to fly up to the top of it, but that was the extent of my use for flying. It was only a very minor time savor.
MPS is one of the mods that is removed before I even create a new world on any SP game.
If I were on a server with it on, I wouldn't use it. Just like I won't use IC stuff. I would never use UU matter, or a quantum suit, nano saber...., or the portal guns/gravity guns.
There are just things I don't like in MC and I won't use, even if everybody else is using them.
You could stick me on a server where every other player on the server has Admin privileges along with complete WorldEdit access and I am nothing but a basic player and it wouldn't bother me one bit.
Just because someone can fly or has more resources than me or can do things that I can't do doesn't mean that I am not enjoying myself or having fun.
Now, if you were playing on say a "Hunger Games" server, that would be different. In that type of environment, where the entire object of the game is to kill all the other players, having an advantage like that would make play unbalanced.
But outside of an artificially enforced competitive environment, other people having stuff that someone else doesn't is meaningless, unless you happen to be someone who thinks that the grass is always greener on the other side.
I personally make my own fun.