Do people really think Button is useless? Personally I've found that it can be the difference between finishing off a tank and not.
Well, it
can, but this situation is still pretty damn rare.
What needs to happen for Button to make an appreciable difference:
1. The vehicle needs to be close enough to the Guards for the vehicle to not move out of its radius real fast. Unlikely, since nearly all vehicles are easily much faster than infantry.
1.i. The vehicle probably needs to be afflicted with engine damage too since a vehicle will probably be able to reverse out of a point-blank button by the time most AT weapons would reload anyway.
2. The vehicle needs enough AT firing at it that it would die with the Button's aid but
not too much that the Button is superfluous. Unlikely in both cases since it's pretty hard to get just enough AT so that a medium+ tank will die within a Button's duration (also probably related to the first point) but not without it, getting that much AT against a heavy tank is pretty unlikely because they're heavy tanks, and getting precisely just enough AT against a light vehicle is also pretty unlikely since they die really friggin' fast.
3. The vehicle needs to be firing at the AT to make the fire-rate reduction useful. Somewhat more likely, but it also relies a bit on the second point since if you've got more than just enough AT for the situation the fire-rate reduction probably won't matter too much.
4. The Guards need to not get wrecked running at a tank anyway, which rather relies on your opponent messing up horribly which is of course, kinda unlikely.
Obviously, this is quite rare compared to the old "might as well be stunlocked" Button (may it RIP in pieces, the pain in the arse) that automatically makes the situation bad for any vehicle while there's other AT around.
And oh man I would love it if DP-28s gave volley fire instead/in addition to Button.
Well, it'd probably stand a chance of being useful at least once in a given match considering people generally get DP-28s on Guards compared to REs getting BARs being a lot less likely, but the "Die really fast to maybe suppress" button would still strike me as usually dubious.