I see that, yeah. They still need days off, or at least at DH, to keep them from wearing down, and it makes sense for that player to be RHH. So it’s a small role, and maybe it should just be filled in house by Pablo Reyes or Bobby Dalbec. But if Solano were game for a role backing up three infield positions and probably getting a few DH reps himself, I’d be interested.
Sort of thinking out loud here to clarify a bit, but there are only really 13 roster spots, and so, in the broadest sense, 13 roles. You have your starting C, 1B, 2B, 3B, SS, RF, CF, LF, for 8 spots. 9 is your second catcher (a modern necessity). So that gives you 4 roster spots remaining.
Ideally, you want those 4 players to sub all the non-C roles occasionally. So at least 1 OF and 1 IF. But given that players are not infinitely fungible, as a practical reality you're going to have weaker starters in some areas, either defensively or offensively. So you're more likely to fill the 4 spots with 2 OF and 2 IF - either for platoon hitting, or defense, or both. You could also use one as a dedicated DH, or a DH who can take the field in one or more positions.
Here, we have (essentially) 1 of the 4 already taken by Yoshida, if you view him as a half-DH, half-OF (instead of one of the 3 OF starters.) Because Yoshida is limited in the OF, the 2nd of the 4 should go to a backup OF who can play center (or all positions). That's basically Refsnyder, who is a platoon bat as well, mitigating against Abreu. Assuming Yoshida (and Abureu) hit, that's pretty good construction right there. And if they don't, it's not like Refsnyder will be wasted.
So at this point, we have 2 spots left and we're without any IF coverage. We need someone to spell the defensively challenging IF positions (no matter who our starters are). That looks to be Reyes, who is a RHH who in a good year might be a league average bat. (But shouldn't be a Hernandez/Chang black hole in a bad year.)
So that leaves #4.
So, if I ignored the roster apart from the starters, and selected someone for IF coverage, I'd probably want a +defensive 3B player who could also cover one or more of the IF positions. A RHH Refsnyderian bat would do, if I were pairing with Devers and Casas, but a league average normal bat would probably also work. The first problem is finding a guy who'll fit all those criteria yet who won't be starting elsewhere.
The second problem is that every game you play Yoshida at DH, you're improving the OF. So that means if you use spot #4 for a plus bat, you'll have to find ways of getting that player into the game. And there, we have the logical forks - if the bat is so good to demand it (and the defense is not bad), you're basically looking at a starting player. Unless they're a super-sub plus bat, and those types are rare. Otherwise you're trading down the offense of Devers and Casas for an uptick on defense. A significant one on Dever's part, perhaps.