The 100% guaranteed engine damage on medium and heavy tanks caused by Fausts and AT-nades just rewarded lazy or careless players who didn't manage to build up a system of AT-options.
When a Tank broke through they could just grab one of their t0/1 units and absorb the assault by killing the tanks engine.
Stuff like that is still possible but it's not that likely to happen anymore which is good because it forces people to use combined AT-systems.
Holding off a breakthrough and interrupting Tank assaults, that's waht mines are there for.
not really though. faust/at-nades punished a lazy or careless player that drove his tank into the enemy lines unsupported. they will not kill the tank (unless the player has infinite ammo). you will still need something that can kill the tank off.
if you support your tank(s) adequately, they might be able to get off a faust/at-nade, but you will be able to repair it before he will have the opportunity to finish it off.
the way it is right now, where you have no reliable way of slowing down a heavy tank (other than button, mines don't count since your opponent has to actively drive over them), it gets pretty hard to trap enemy tanks without a vastly superior force.
the bottom line is: fausts/at-nades always had counterplay: kiting (the homing missile thing is bad imho, but that is another story). the nerf effectively makes the game more forgiving for less skilled players that are not good enough to kite, by giving them a chance at another shot of trying to kite away. i don't feel like that is a good change.