I agree - it is too much.
You can't defend against PAs, besides having all your units in Acropolis. But what if you want to have defense in your city for PvP points ...
100 PAs will wipe most of the army of many players, and they may not even be online.
This is not balanced.
If the counter argument is ... "How many players do you know that send 100 PAs per day ...", well, exactly, why can't you reduce the limit then if almost nobody sends that many? It will save a few players their troops, because there are players who will bomb your city with 100 PAs out there, and this will save those players' troops.