Mobile champs that actually deal damage(not including supports and tanks) don't have much utility. If you take a look at damage dealers with mobility:Zed has a shitty slow, Katarina has nothing,Talon has a shitty slow, Yasuo has a knock up , Rengar has a root that he needs to sacrifice damage in order to use it or a slow, kha'zix has a slow only if he evolves his w,Graves has no cc, Akali has a slow in her w that is barely even usable,Diana has a small knock up etc.
If you take a look at purely immobile champs:Lux has a bit of a slow, a root and a shield, syndra has a stun and a slow,Cassiopeia has a slow, a root and a stun,TF has a point and click stun with an ult that gives vision,veigar has a stun which is also a zoning tool, Orianna has a shield, a slow and a knockup(or w/e the hell shockwave counts as),Fiddle has a fear and a silence and so it goes on.
There are a few exceptions, like ekko and irelia who are mobile, do a lot of damage and also have cc, but those are just awful designs.
And after all, most of the time the damage output of both categories is the same, unless someone gets fed. You may think that zed does more damage than per say orianna, but zed does his one rotation in a teamfight and then does nothing for the rest of it, while orianna has a 1.5 second cd q that she can spam during the fight as well as her other abilities.
Idk why I even bother explaining this, boards don't like the use of logical arguments anyway but why not