It may be lousy that the Mets pulled off this trade, but I don't think anyone trying to build the Nats into a 2021-22 contender thought the Nats would get either of this guys. Now, unless you think the Mets are unbeatable (like the NYY were in the AL East going into last year
), your key acquisitions are still the same: for about $40MM, you can get a couple of minor complementary players (Zimm and a backup catcher), a major bullpen arm (preferably Hand, but there might be others), deal for a below Lindor-level bat (say, Suarez) giving up a young cost controlled guy with upside and near MLB (Garcia? Kieboom?) and any pitching prospect not named Rutledge or Cavalli (or Lara if you can), and then have enough money for a $15MM bat. That leaves you short on a rotation piece, I think, but you only need something at the Hellickson level or a touch better. Maybe you can't get all of that, but it is not white flag time. Time to deal a Turner is if we spend for this and we have negative luck.
EDIT - Brantley's estimated next contract AAV on FG is $15MM. He's probably well within any reasonable budget. You still have some decisions, but even with the current on boards plus a cheap RZ, you would have a top 5 of Turner, Brantley, Castro, Soto, Bell/ RZ. You can go to war with that, even if you don't pick up another major bat beyond Brantley.