The only thing I can suggest is that Poch is managing the subs in a way that allows them to be rotated to play the next game.
Poch manages a squad with multiple injury prone players. It's not just Dembele and Wanyama but also Lamela, winks and Rose. There have also been long term injuries suffered by Verts and Toby. Yet somehow Poch gets us punching above our weight.
IMHO everything he does is highly considered. Do you not think if you and I ( I am assuming you are not a football manager here) can see a change is needed he can't? Yes occasionally he may get it wrong. But the fine tuning of our squad to wring out every last bit of quality means that even what seems like a small detail such as bringing on a player for a few minutes in a game, may adversely affect their energy levels in the next game.
Fans who criticise Poch's'lack of substitutions should compare Poch to a manager like Unai Emery who is much more proactive with his use of subs but is 7 points behind us in the table.
I wish we didn't have quite so many injury prone players because we end up, at least once a season, in exactly this situation.
Again, with all due respect, this is arguing with respect to authority. The fact that Poch is clearly a more adept manager than me does not mean that he does not mistakes and that he is perfect. Nobody is perfect. Like I said, all managers at top clubs will have access to this kind of data. Can I, a mere mortal, or you, the same, criticise Mourinho? Am I a better manager than him? Then Emery? Than Klopp? Even than Wagner or Warnock? No, clearly not. But not all 20 of these managers are walking around making perfect decisions all the time. Look at how much criticism Mourinho got on this board for example. Yet this is a man who, by Poch's age, had won 2 Portuguese titles, a uefa cup, a champions league, 2 premier leagues, an fa Cup, 2 league cups, a serie A and was starting the season he'd win an unprecedented treble with Inter. Does that mean I can't think that him constantly talking down his players in public and downplaying man utds pedigree in Europe is right or good? No.
Emery is a manager in the first season of his new job, with the 6th best squad of the league and who hasn't done a bad job so far. It's probably as unfair to judge him on his first season, just as it was to say pochs work in his first would reflect his subsequent work. And similarly, emery has won a lot of trophies, including at seville, so again, by that logic, who are we to criticise him and the sports scientists he's worked with?