It IS slanted toward Mr. 4th place. I suspect it may be because Mr. 55 Games Back has given up and does not care much.
Thames is, for the first time in his career, getting a shot at playing every day. I am not confident he keeps up his torrid pace. He has a 3-year history of significantly slowing down the second half of the season. But again, this is his first shot at playing against both righties and lefties. Banks has minimal value. Soto is a stud at catcher.
But...you have three solid players in Bay, Drew and Soria have little comparable downside other than Drew's injury history (and his possible move to #2 in the order...less RBI chances).
For all that...it is not so overwhelmingly lopsided to warrant a veto (though I admit that it does legitimize a discussion). You would be setting a very tricky precedent by intervening; you even admit that part of your motivation is the worry of a competitor improving. You will most likely find that the next trade will be close again - do you veto that one, too? No? Why not? You veto it, too? But then, who gets to trade? If you are in the race, can you not trade anymore? These will be the questions. The trade veto power - in my opinion - should be enacted when it is a grossly lopsided example of collusion. You'll know it when you see it and you won't have to ask us meatheads. But anyway, do you really think that he is improving all that much? He gets his closer, but who will he play at catcher now?
My opinion comes from the mindset of allowing managers to run their team as they see fit. I am therefore careful who I allow into my league(s), and also know that in similar cases to this, ANY others could have made the same deals with the "cellar dwellers" who are interested in dealing cheap. Gotta beat Mr. 4th place to the punch. You never know...maybe the guy has got more to unload and you can make a deal of your own... This is not often a popular opinion, however.