Serie A is not in decline. Serie A is stagnating as number 4 in the world for some years now. That's a difference. Juventus isn't though, we are improving on all levels. Ultimately the club is for a player more important than the league, just look at PSG. And that Dybala already plays in Serie A is an advantage for us.
Also while Dybala is a great player it's not like he is a once in a generation player everyone wants to sign under any circumstance. We definitely have a chance if we are ready to invest in him heavily.