To clarify:
THE BASIC PROBLEM, that one player experiences no rollbacks and the other player experiences severe rollbacks, AFFECTS BOTH PC AND PS4.
It is likely that if you are consistently having flawless matches on medium- or high-ping connections, the other player is experiencing all the rollbacks.
The culprit is not the alt-tab, it's the fact that the netcode does not handle time-syncing between the two machines properly. One machine can end up "ahead" of the other. That's the basis of the problem, because when one player is ahead, they are constantly getting inputs from the other player "late" so they are rolling back a lot, whereas the other player is usually getting all the inputs they need when they need them, and doesn't roll back at all. If the game properly handled syncing, like GGPO does, then the other player's game would slow down for a microscopic moment to correct for your alt-tab hiccup, and both players would continue to experience about half of the possible rollbacks each.
Alt-tab allows PC players to shift the situation to their advantage, but that is not the actual problem! Even if you are only playing against PS4 players, this problem can and will still happen to you.