Not new, and it's something he's been stubborn about for a very long time now. I might be wrong about this, but I think I saw a graphic a while back that said that we were the last team to use our subs (per ninety minutes) in the entire top six - we routinely wait until 70 minutes plus to bring ours on.
It's a bit puzzling, to be honest. He lunches with Fergie to try and learn from him - but Fergie was a master at using subs to change a game, and didn't give a damn if the players felt unhappy about being dragged off. If a United player played like ours did today, he was coming off - no ifs and buts, he was useless and everyone would know it when the board went up. And that worked.
Poch is the exact opposite in-game - he'll never bring anybody off even if we're being utterly massacred. I suppose that it's because of changing times - footballers are more sensitive and demanding these days. Or maybe it's just the youth of these players relative to the ones late-era Fergie used to use. But, despite that, those are constraints other managers have, too - and I don't think any of them outright hate early substitutions as much as Poch does.