I agree with everything you're saying, players simply need time to develop and grow. We've got a very good crop of youngsters now, although they'd benefit from having players they can rotate with to ease the burden a little.
I assume you're talking about Foden in the last sentence. He's done superbly for a few years now so these performances aren't a new thing. People were frustrated at Pep for being conservative with his minutes but he's been massively lauded and hyped here for about 4 years now. In any case it's unfair to expect every young talent to end up the best in the world in their position, realistically it just rarely happens.
If it does, great. If it doesn't, we've got a very good and useful squad player for minimal fee.
My point, which I argued a bit in the Champions League thread, is that Pep probably was right in being conservative with Foden.
We can of course never know, as there is only one outcome available to us, but this is my persuasion.
I am never frustrated when Pep is handling young players like that - he did the same with Thiago, Kimmich and many more. It's a sign he believes in them and that they will become great, if they stay with him.
I believe Pedri would play maybe 1/3 of the minutes he did under Koeman if Pep was here this year. I think he would be a perfect player where Pep would keep praising him, playing him now and then, focus very much on his habits. There would be training and match footage where he yells in his face because he was not receiving with the right foot, not positioned in the exact correct spot or running at the right time when they're 4-0 up, etc.
Koeman started yelling on Mingueza, then subbed him, then didn't shake his hand, then played him one game but then again put him on the bench the game after, when Mingueza did something he didn't like...
I think it's easy to forget that football players are very lazy, and don't care so much about the details. The ones succeeding are often very talented, and didn't need to think very much about the "small" things. There was a famous clip where Pep explained to Sterling how to recieve the ball, and it was made out to be some genious instruction. It's the same thing that is told to 12y.o kids! It was needed with Sterling, and with many smarter players too, but the big thing is to just be a perfectionist with these habits, and tell the players that they are doing wrong.
It is true we cannot know very much about what is done with Pedri or any other players behind closed doors, but this is my impression from the outside.