Lol have they even been watching the right team? We haven't tried to play 4 at the back regularly ±in any meaningful way since O'Neil's first couple of games in charge last season. When we had a CB injury crisis he tried a back four with Lemina at home to Bournemouth but it didn't really work so he went back to a 3 until he was sacked.
The big difference VP has made is we have looked a lot more compact and organised, and aren't as easy to play through the centre of midfield. And we've stopped conceding so many set-piece goals. He hasn't changed the formation whatsoever.