He isn't safe and never was, the fact that we did lose that setup puts us at risk. Yes it's possible to do a JabJab spaced to Usmash, however that isn't guaranteed until higher percentages ranging from 120-150 in which you are losing to rage.
The fact is shielding is pretty much safe against Fox, due to the lack of throw setups.
So Fox has to use his double edged speed as his weapon to bait and punish, however against cautions opponents, this can be turned against you, hence double edged. Nair isn't really safe on shield, as soon as they've taken the hit they can go in for a grab on you or whatever options X character has and is able to react to.
Fox was / is a combo monster from the setups he had, but as all of them are attacks shield is strong due to the "Triangle" of Sm4sh being Atack > Grab < Shield > Attack.
I'd say Ftilt is hard to punish on shield as well due to how fast it is, but it does move you forward if memory serves.
Like Nakat put it into words "Frame trap character" but not everyone is going to fall for the same trick twice.
Wow presumptuous much? You really are a work of art aren't you.
You and G-sword should go form the **** talkers club, but maybe there isn't room for him due to how inflated your ego is /sigh.