shaco needs to ulti in order to jump.
Deceive is quite possible the best QWE mobility skill in the game.
It's Shaco's Q. Which isn't his ultimate.
Which is why I mentioned Shaco as an old champion that's extremely mobile. He's one of the most irritating assassins to chase down.
Jax's 6 second CD leap (pre CDR) also isn't "a long cooldown". It's one of the lowest CD mobility skills in the game.
Mobility creep is not about having anything that let you move differently from base MS, it's when this mobility becomes a part of the way of playing inherent of for the champion and frustrating for whover plays against it.
That's not mobility creep.
Mobility Creep is a type of power creep. With mobility. Others have covered what power creep is in this thread pretty well.
What you're describing sounds a lot more like "mobility should never be a key part of a champion's play style". Which is a fairly awkward stance to take considering LoL has over 100 unique champions with different play styles.
Mobility isn't a quality devoid of counter-balance, it largely fullfills the same ultimate goal of defense, range, and CC. Allowing a champion to survive long enough to get their job done.
If a champion is like, say, Riven - where she has incredibly limited defense, range, and CC - she should probably be mobile.