They do need a 1b, but unless SF offers up Bryce Eldridge, doubtful they use Marte to get someone. Triston Casas is basically a repeat of their current Pavin Smith.
I looked at RR on Fangraphs, which is usually pretty accurate. Their starting OF was Blaze Alexander in LF, Alex Thomas in CF, and Corbin Carroll in RF. Carroll is an MVP candidate, and Thomas is passable due to his defense. Alexander? I’d say FG is just filling gaps wuth best available here. Duran, whose WAR values are comparable to Marte, does fill their OF. Not sure if they view Alexander as a defensive solution in the INF, but it is a possibility. So basically they could swap out Marte (10.9 fWAR and 11.6bWAR in the last two years) for Duran (10.8 fWAR, 13.4bWAR in the last two years) and gain Bello along with it. Marte does have a good contract, but Duran is still younger and cheaper. Fewer years left, but doubtful AZ considers losing Marte at 36 and 37 a deal breaker.
Does it make sense? Sure on one level. But it all depends what direction Hazen wants. One point in Boston’s favor is Hazen might have favorable opinions on both players. Of course, he might also hate them both with the white hot passion of 1,000 August suns, I suppose…