He's 21, compared to Mahrez who is 27, so less experienced, and less mature.
Also you're saying above that Aguero needs to be playing to get back to form, but isn't this the same for Jesus, who just has got back to form, and therefore needs to be playing to stay in it ?
The reality is, it not quite so black and white, Mahrez needs to learn yes, but while he is sometimes good, he often isn't at the moment, and he's not consistent enough to keep Sterling or Sane out (or Bernardo), and his brief sting in the centre wasn't even close to good enough. Jesus has worked hard and kept going whilst Sergio has been out, and right after he's found some scoring form (the rest of his game was good anyway), you want him out again, when in fact he needed (needs) a run of games to keep his, so its hard to see the argument that the experienced Mahrez should be playing to get into form, and the younger Jesus should just be in form whenever asked to be.
We have a very talented squad, and it all needs to be used equally well, and it will be, with a game every 3 or 4 days for the next 8 weeks.