Gabriel is coming along just fine. He's more than carrying his weight playing under the greatest striker in PL history. He's getting a PL goal every 119 minutes and in that same time frame Kun is getting one in 107. Until this season (and some of last) he was levels ahead of Aguero in doing the gritty stuff from the front. He's had a few injuries and a good chunk of his minutes have come off the bench. He's had to acclimate to a new country, culture, and climate. We don't need him to play like Ronaldo or to score the types of goals that Aguero does. He's not scoring the goals that Aguero is famous for because he doesn't attempt to play like Aguero (rightfully so). Aguero is more aggressive with his shot selection and takes on defenders at a much higher rate so of course he'l score more attractive goals. Both of them are playing for the team and not the individual.
We know Aguero is without a doubt a top 3 striker in PL history. According to many Jesus needs to improve his finishing, he can't head the ball, and he's apparently been out of form and lost that spark that he showed up with. If those things are true then why is the greatest in history getting about 0.85 goals a game and Jesus getting around 0.80 since Jesus arrival?
He's fine and he's better than he appears.