I think Dembele needs to make a bigger contribution to the team. He has made 2 assists so far in the Poland and Australia matches. There is no goals scored by him so far. He has a really good talent actually but maybe he isn't able to take much responsibility in the absence of Mbappe especially. Dembele is more active while playing for Barcelona for example. But when you have a bigger star player among your teammates you might need to be more careful with your game. France haven't had any problem about this topic so far anyway.
Benzema's absence hasn't also been felt much as Giroud has been very successful. Benzema is still an important player for France of course but this shows that he is replaceable as well now.
Obviously Mbappe is more important than Dembele but I think the position of Dembele and Mbappe is different because it seems like Dembele plays more on the right and Mbappe on the left. With that difference I think it doesn't matter if both are played at the same time, and it also happened in this moment but Dembele is indeed often substituted and it seems very rarely Dembele plays the full 90 minutes.
Dembele and Mbappe are the main choices at their respective clubs, so it's not surprising that in the French national team at this World Cup moment Dembele and Mbappe are always the first choice in the starting eleven.
Regarding Benzema, at first it was predicted that France would have difficulties due to Benzema's absence but the fact did not happen, maybe because Benzema's absence also made Giroud able to show his quality as an old player who is still very productive.
It's just that maybe this is the last chance for Benzema to play in the World Cup, but in reality Benzema can't play because he's still suffering from an injury even though Benzema is in his best performance after getting the Ballon d'Or too.