That first sentence is just hyperbole. The team is not weakened let alone considerably when jesus starts instead of aguero. If one thing the past season should've shown or taught anyone it would be that its the system that makes this side more so than any specific players' quality(outside of probably ederson).
Going into the season if anyone told you de-bruyne would be missing for large portions of the season through injury and that fernandinho would also miss most of the business end of it through injury would you have envisioned a treble winning season. A team that went through most of the season fighting for 4 competitions with zinchecko as its main left back.
Now does the side lose something without the likes of de-bruyne, fernandinho and even sane in the side, yes without a doubt. But does that make it weakened in any considerable way, no. The style of play never changes, they just find another way to dominate and create chances.
Aguero is a world class player and the current version of him is the best he's ever been, He's always been a deadly finisher and poacher in the box with immense dribbling ability but his link up play, pressing and awareness have all improved immensely from what they were before pep arrived. He's rightly cemented himself as the 1st choice striker this season after a period of uncertainty and him getting adapted to peps style of play during his first 2 seasons. Ironically despite still scoring at a good rate pep seemed to trust jesus more in his second season and there were some questioning(including even me) if he would ever adapt to the way pep wanted him to play which changed this season with him being the all-rounder pep wants.
That brings it to my next point. Gabriel jesus is not yet the same quality as aguero but is still a very good young player with intelligence and awareness of space beyond his years. That combined with his high work rate, good link-up play and technical ability means the team loses little if anything when he starts and is certainly not weakened. What if I told you the team scores at around the same rate of goals regardless of who starts between them would it be a surprise to you.
Basically to summarise, the team could win 5-0 with jesus starting and he may score just the one goal but would still be an important cog of the system due to his intelligence and movement allowing more space for the other attacking players to contribute more while in another instance with the same 5-0 scoreline but with aguero starting, aguero might score 4 due to his natural poaching ability and finishing. The team would win both games, the two players would contribute in their own separate ways to that victory and the fact that aguero scored the 4 goals compared to jesus' 1 doesn't mean the team were weakened as a result. It just means one has other qualities that benefits the team and system in its own way.
Not only do I believe jesus is a more than capable understudy, I also believe at just 22 he has a lot of room to improve where he would be one of the best strikers in the world and lead the team to many trophies. I don't get this idea that he's not good enough and the club needs to spend big to replace aguero.
