Well for starters, you'd get less goals that's for sure. Griezmann has 3x the non-penalty goals, and this is a shit season for him. Secondly if all we're going to do is get second-rate attacking midfielders for free then the wages are no longer an issue.
If this is a shit season for Griezmann, then what was last season?
I'd say that's his level in a Barcelona team. We are talking about a player who joined the club in his best years talking about age. Looks like he had his prime in his younger days though and never will be a fit at the club. Griezmann is better than Depay, but he is earning 3 times of what Coutinho is getting and if there is a chance of selling Griezmann the club should take it. Club still needs to reduce salaries to comply with salary cap rules.
Not really a fan of Depay joining Barca, at least not as fixed starting player, but he is free and on much lower wages than Griezmann and even Coutinho. He wouldn't be my first choice either, but he is probably the best we can get this summer. Doubt the club will offer him high salary, so he even should have some resale value. He worked well as #9 when Koeman was NT coach and offers some physicality.
Having said that, I doubt the club is trying to replace Griezmann or Coutinho with Depay. What they are trying to do will be replacing Braithwaite with Depay, I'd guess.