You could say the same think about Petersson. Not many people saw him as a top 5 center. He has drafted at 5.
I don't see your point. He wasn't seen as a top 5 center in the league, but he still became one. Jason Robertson was not seen as one of the best wingers in the league, does that mean you wouldn't trade Mesar for him since Mesar was drafted higher and also isn't seen as one of the best wingers in the league?
You also get a very young and loyal player in Celebrini. He will be only 18 years old next season vs 26 years old for EP. Lower contract. Growing up with our young core (Slaf, Hutson, Ghule, Reinbacher....).
Unless Celebrini goes full Eric Lindros on us. I don't see us ever trading Celebrini for EP.
EP is from the same draft class as Suzuki, he's still in his prime and will be for a while. Lower contract doesn't mean much when it's highly unlikely Celebrini's ELC performance comes close to what EP does. That also includes Suzuki though. Lightning won the cup with 30 year old Stamkos, 29 year old Hedman, but also 24 year old Point and 31 year old McDonagh as key guys. Your core guys won't be similarly aged.
I don't see EP even being interested in MTL so this is all fantasy talk anyways.