Where is he going to play? His best role would be were Mitoma plays, and I don't think he's better than Mitoma right now.
Then there's the striker, where if I'm not mistaken he has to fight the spot vs Evan Ferguson (better prospect for Brighton than Ansu), and the occasional game by Welbeck who is worse, but maybe better than Ansu leading the line up top (he plays better as a second striker or left winger).
It would be a great signing for a reasonable fee, if he were fit and with how well you've developed talent lately. But as a loan, I don't think he nails a starting spot right away and improves the team vastly, great depth option, but with his demands of being a starter on Barcelona, a couple games on the bench at Brighton could have him creating a problem.