You have to take his FG % in the context of both the shots he gets off and the ones he doesn't get off because: (a) the ball is regularly stripped while he's positioning the defender to get his shot off (teams that scout him well do this effectively and it kills us), and (b) on plays where it's passed back out of a double team, Fous uses a lot of clock for positioning and then he is a little slow to recognize the double team and get the ball out to his teammates. I think he's probably just being careful not to get a TO when he's passing it back out, which I appreciate, but he telegraphs it big time and that gives the defense time to recover and close out on open shooters. So instead of passing the ball out to a wide open shooter, it regularly goes out to a player that is covered who now has ten seconds or less on the shot clock to create their own shot because there's not time for the offense to reset.
Let me reiterate that Fous is extremely talented as a scorer in the low block (I would even say special) and if he can be more efficient in recognizing the double team and quickly making the pass to the open shooter then he would be deadly for opposing defenses. Because his kick out passing is not as crisp, he's a bit of a liability when he's not able to get his shot off. So I think he's the perfect guy to come in off the bench with significant minutes to maintain continuity if things are going well (or give a "change of pace" spark if not). As a bench player, teams are less likely to hone in on his weaknesses to shut him down and/or double team him, so I think he'll really continue to thrive in that role. Keita makes more sense to me as a starter because he's a little stronger on D as a rim protector and the starting five don't need Fous' offense as much as the bench players do. That's just my 2 cents on it.