I tend to try to be curious and think through all the reasons for a decision I don't understand, especially when it comes to ostensibly smart front offices making them. But there's two things that really tip me to Mervis needing to come up and play most days.
One is that Hosmer is not delivering the profile that's expected. I don't mean from a raw production, wRC+ level, though he's not been good on that front. I mean in terms of optimizing him relative to alternatives he's regressing. His K rate is up to 23.5%, which while not brutal in 2023 is far from the contact heavy 16-17% he'd been at for years. He's also giving away value on the margins. The baserunning mistake in Miami, the unearned run on the bobble yesterday, this isn't the work of a guy who's doing everything but hit for 1B power, it's a guy who's been below average across the board.
But the other reason that really pushes things over the line for me is Rios. I don't know how I overlooked it until yesterday, but he's played two (2) innings at 3B this year, meaning all other PT has been in the Hosmer zone of PH/DH. I like Rios and would be curious to see him play more, though with Wisdom's torrid start and Rios not capitalizing on small opportunities I understand it. But he is on the roster and has an option, which means you can make several risk free changes to the status quo. Worried about Mervis simply being unplayable for unknown reasons? Swap the PT between Rios and Hosmer so you know what you have in Rios. Not ready to kick Hosmer to the curb? Option Rios for Mervis and give him Hosmer's previous share of time while Hosmer becomes the PH/matchup DH Rios was. If Mervis isn't ready or creates some other imbalance you haven't lost any roster flexibility.
I suspect there's a small disconnect that's creating the current situation between Ross and the Front Office. Reading between the lines, Ross trusts Hosmer more and Rios less than the FO, but the FO doesn't see that as a big enough deal to do something they are not comfortable with in the moment(bringing up Mervis for Hosmer or Rios). But we're at that point, Hosmer is getting about 75-80% of possible playing time at 1B/DH while Rios is getting ~20%. It can or cannot involve Mervis, and it can or cannot involve Hosmer getting cut, but Hosmer's PT has to go down.