Iniesta is one of the all time great midfielders. Foden has barely played as a midfielder so far in his career.
Foden is better than Iniesta at scoring goals, although Iniesta like Zidane scored vital goals in huge games for club and country. But if scoring goals was the main factor in determining class, then Lampard was superior to Iniesta and Zidane, which he clearly wasn't.
Foden's main problems this season are two.
First, he's been average creativity wise, which isn't great for a genuine No 10. He has as many assists as Gvardiol, and fewer assists to Haaland than Gvardiol. But Foden has sort of compensated it with goals. 7 league goals in the 1st half of the season is really good. He's been like a very good forward playing in midfield
Foden's second problem is that he has been anonymous in the big games, especially away from home. He worked hard but wasn't really in the game against Arsenal and Real. You must be involved if you are a midfielder. Old Bernie has been more helpful in midfield than him.
So, he has to improve creativity wise and be more involved in big games (away from home). Cherki has been here a few months and looks better in tough games.