But it is comparable for mediums and below. They can equip one or two, which gives more flexibility. With mediums, piats could be even better as commandos are more durable and will usually have a chance to shoot more rounds before they need to retreat. For heavies it isn't too bad either. Imo it is absolutely comparable in real game scenarios when such units often just add up their damage to other at sources.
No, its not, because axis mediums have much higher armor then allied ones and shrecks have 100% pen against all but few USF doctrinal ones.
No one in his right mind will ever equip 1 piat on anything-yes, you can do it, no you should not do it, because you aren't going to be able to kill even kubel and even pwerfer or stuka will have a chance to run from it.
You're grasping at straws while avoiding facts.
Its time to stop making excuses and start learning the game.
Check steam forums, there is one eager there to give tutorials and lessons to newbies.