I am certain you didn't mean a complete escape - most people who are very pro mobility aren't looking for anything ridiculous; but consider something really quick - ANY level of escape can make a champion strictly better than a champion without an escape/move steroid.
My complaint is that older champions, fun ones, who were made before mobility creep, are almost a joke now. They can't catch champions who do have high mobility or get away.
As an example: I play top lane as a main. I love to play AD Sion. Normally, in late game I do amazing damage, and can use ghostblade/Zephyr/Ghost to avoid being kited. I can be 4 levels over a Lucian/Teemo/Quinn/Vayne, with considerably better items. I will be kited into the dirt.
I have been outrun on Singed / Hecarim / at one point even Rammus, cause he was really ahead (specifically Lucian here)
It's not that it's inherently broken either - look at Graves. The problem is when A high mobility champion has, well...HIGH mobility AND no reason to ever come near you. League is a game about deciding when to fight, strategy, etc. - champions like Lucian, especially the way he was, promote safe, defensive game play where the strategy is just not fight. Ok, thats fine, most adcs are like that....but good lord, you cannot catch him.
Basically, the LAST thing Riot needs to do, for ANY champion, is to specifically insure that they have an ability that grants an "escape" - If you dive and don't need a summoner spell, or are really pushed -> get ganked with no ward -> and can still get away fine, there is a SERIOUS problem there.
This is at least my opinion, you don't have to share it.