The mine meta just kinda invalidates your point. Mines exist on only Engineer yet it's still a problem.
No it just reinforces the point that quantity matters. Yes only engineers have it, but when you can just place 3 of them every time you spawn and they persist, then that becomes a problem. If a single class can make a difference, then adding it to another class has an even bigger impact.
I'm now forced to play Recon because they are the only class with C4.
This is a good thing. It means you need to make choices about which class you play.
Support has always been able to resupply themselves with infinite C4 similar to what they could do in both BF3, BF4, Battlefield 2042, and probably lots of other Battlefield games.
Just because it has been done before, doesn't mean that it's a good thing.