The reason why they can't just change the design of the pilots is that their silhouettes need to be distinct enough to be recognizable on the spot. If you see a pilot you should be able to immediately discern what ability they can use.
That said I'm all in for a redesign of some pilot types, as they look too similar right now. I always felt like some of the designs in this game are weak, might as well bring it up now.
Respawn appears to apply a "rule of 2" where there are usually two designs resembling each other. A-Wall and Cloak, Stim and phase. Holopilot, Grapple and to a degree Pulseblade also look very similar to each other
Titans are handled a bit better but the rule also applies here.
They are more easily recognisable as they have more distinct features and are simply bigger on the screen, but titans of the same weightclass look very similar. You notice that even moreso when you break them down to their silhouettes.
This is probably also why the Prime Titans aren't all that outrageously designed but stick close to the original. You put those silhouettes behind 3 layers of dust on a bustling map and you'll start running into problems. I'm G4.30, put a fair amount of time into the game now, but I occasionally still mistake Ion for Tone or vice versa.
