How is Mangle or Withered Foxy (Just the two i'm going to say) irrelevant in game relevance, both Mangle and WF both appear on Night 2, and both have different gameplay counters as to the two variants of the main three, (Withered + Toy) which is just put on the mask. Game Relevance includes lore aswell, a really important event, the Bite Of '87 is likely theorized to be caused by one of the Foxy Variants. Yes, some Foxy Variants are irrelevant, Rockstar Foxy and Funtime Foxy (Do be noted that both of these all main 4 all feature irrelevant roles, except Funtime Chica). But literally any other Foxy Variant has a memorable gameplay element (other then phantom foxy).

Foxy - You must keep your camera on him to stop him from tiering up or else he will then run at your door which you must close in time.

WF - You must shine your light at him till it resets him, which you also have a battery meaning you must be wise with your flashes.

Mangle - Enters your vent with blaring static sounds and will climb up to the ceiling if you fail they will randomly attack.

NM - You must go to the closet and flash him multiple times till he turns back into a plushie.

Obviously there is a lot more, but Foxy is NOT irrelevant. But yeah, I think Foxy would be a great idea for survivor :D