I'm not a huge fan of Rosario - only included him because the Indians reportedly had interest last winter in Lindor negotiations - I'd rather do Davis+Nimmo+prospects.
Even if this isn't the trade to make, you're going to need at least some immediate help if you're serious about winning, and it doesn't sound like it'll happen through free agency aside from minor league deals. This is what we're staring at right now - Roberto Perez at catcher, Josh Naylor at 1B or corner OF, Jose at 3B, and Reyes at DH. That's it.
I'm high on Nolan Jones and hope he fills a role, but beyond that I'm not excited about the internal options that would be ready in 2021.
Jake Bauers, Daniel Johnson, Bobby Bradley, Yu Chang, Mike Freeman, Delino DeShields Jr, Jordan Luplow, Oscar Mercado, Bradley Zimmer, Tyler Naquin...plenty of options, but how many good ones? Only Naquin has proven capable of being an every day player when healthy, and he might get non-tendered. Luplow is a platoon player, Bradley/Bauers look like AAAA players, Freeman is a utility guy. I like Daniel Johnson and would be OK with him getting a shot. Yu Chang too, although the Indians don't seem to think highly of him IMO.
That's a lot to say that the Mets deal isn't perfect, but if you explore the landscape and all you get are offers of players that are several years away, I'm not sure you can make that deal and still say you're trying to win. Of course I'd prefer Dylan Carlson, Jo Adell, Alec Bohm, and other young, cheap, controllable but ML-ready talent. I'm just not sure guys like that will be available.