Witness inflation is done on the joint transaction itself. Unconfirmed ancestors are not needed for this attack vector.
v3 does prevent pinning, but witness inflation can still be used with a single 1000 vB descendant to inflate the RBF cost for the victim. Doing this repeatedly can burn the victim’s funds to fees, with no cost to the attacker. Whether this can be done reliably, I’m not sure – the only way to find out is to try such an attack.