I don't think Dombrowski had any prior connection to Merrifield. And I do have some faith that the Phillies wouldn't make this move if their analytics team and manager/hitting coach didn't think it was a good idea. But that was also true of Josh Harrison last year.
I think Marsh loses the most playing time to Merrifield (followed by Sosa when Marsh replaces him in CF). But yeah, if Stott needs a day off it probably goes to Merrifield now. And they've already said they want him to play 3B too.
Sosa was never going to play as much this year as he did last year (when Bohm had to play 1B and neither Ellis nor Clemens ultimately stuck). I just think he makes sense on a team that needs him more, and it doesn't make sense to bring in another RH utility guy (but then it really never made sense to sign the RH Harrison on top of Sosa either. At least Merrifield is more of a proven OF).
I don't think the presence of Rojas in CF is relevant to the ability of Pache vs. Merrifield in LF. Sure, if Merrifield rediscovers his bat, his defense doesn't matter and he'd be more vaulable than a presumably scuffling Pache. But if they are both 85 OPS+ players Pache is better. And I still like Pache's chances of improving and thriving in a part-time platoon role than I do Merrifield's in a broader role, but he's probably better off on another team where he can play CF more too.