You mentioned vacuum before. The amount of at on sov infantry makes a fragile puma have hard time, especially after at guns are out. You really have to be a good player to make it work. Please don't pick statements out of context.
You can use that argument about literally any kind of hardcounter and unit it hardcounters.
And it still doesn't change the fact that one unit counters another.
Puma is also anything but fragile.
1 in 25 small arms shots will pen it, other then that, you need same level of AT you'd need to kill T-70 if you want to get rid of it, except you can't use vehicles, because it counters them.