You're right.
Duda 1.2 WAR
Moreland 0.9 WAR
Alonso 1.5 WAR
Duda and Alonso are better offensive players but Moreland makes up some ground with his glove. But if you think Moreland is going to hit again and is just going through a bad stretch, he is comparable to Duda and Alonso.
The weird thing about Alonso is that his oWAR is impressive (2.5) but not his dWAR (-1.4). In contrast, Moreland's oWAR is 0.6. If the Red Sox think Alonso is a better fielder than his current dWAR would suggest, trading for him would make sense--he is a much better offensive player than Moreland.
But let's say Moreland, Duda, and Alonso are basically the same players in terms of value, where do the Red Sox go in order to improve the offense? The first basemen who are clearly better than Moreland either aren't available or the Red Sox don't have the minor league assets to acquire them, leaving us with the likes of Duda and Alonso.
As such, maybe the Red Sox promote Devers, find a relief pitcher, and that's it. Just hope that guys like Moreland, Benintendi, and Bogaerts hit better over the next three months.