It's called implicit collusion. They are implicitly colluding to skip heavy as a kind of "gentleman's agreement" to make the contest "purer" because they believe they are part of an elite where that is the "code" However, doesn't mean the rest of us are using a CRUTCH when taking Heavy, it's part of the game mechanics

Heavy ammo ruins the game. Especially 3 vs 3 and spawns far too often in 6 vs 6.

Completely subjective. Everyone is under the same conditions therefore it is part of the game and not a crutch