So you get the 6 WAR up front with Marte at a premium cost. With Mayer, you may get more WAR and a controlled cost over a similar term.
If the Sox were all in on winning a WS in '26 or '27, I'd be all for the trade. It just seems like they are one foot in and one foot out. If so, it doesn't make sense to go for the short term guy at the expense of the long term one.