Maybe there don't appear to be any clear holes but that doesn't mean that certain spots can't still be improved/upgraded. Adding another bullpen arm is never a bad idea, for example.
This. I mean, they don't have a lot of holes, but they also don't have a lot of top-of-the-line players that you can really count on, either. Some guys may be playing way over their heads right now. I suspect that's the case with several of them. But the way they're going, and especially at their current salaries and ownership's unwillingness to really go above and beyond in that area right now, I don't know how they improve.
C: Wong is at 142 ops+ with a cannon for an arm. He also makes league minimum. How could they improve on that? McGuire is at 73 ops+ and could be improved, but why bother, with Teel on the fast track for the majors soon. No sense giving up a real asset for a better lefty hitting backup catcher.
1b: Casas returning from injury is the single biggest improvement this team will likely experience in the latter stages of the season. They're not getting another guy, not when Casas should be returning.
2b: Valdez is at 83 ops+, and yeah, he could be improved, but it would be a stopgap, right? They're pretty committed to Grissom moving forward, but even if not him, they've got guys in the minors heading this way as well.
3b: Devers is going nowhere and is one of the best 3b in MLB (not the best defensively of course, but the total package). Tough to improve there, and the cost of getting a 3b who is, overall, better than Devers, isn't worth it.
SS: Hamilton has been a revelation this year, and they have Story returning from injury next year. Oh, and Mayer is on the way.
OF: Duran is a stud. Tough to improve on him right now. Rafaela doesn't hit a ton but he's been improving. Since May 1 he's hitting .275/.305/.419/.724, which isn't bad at all. Over his last 27 games he's at .327/.359/.459/.818, but some of that is smoke and mirrors. And of course he's spectacular in the field. They could get a better player, but at what price? And in RF Abreu is giving them a 122 ops+, while O'Neill has 15 homers and a 146 ops+, and Refsnyder is backing them all up with a 148 ops+. The big area of improvement would be Yoshida. But how to move him, and for what?
SP: A lot of guys who have had good years. Houck is a stud - can't really do much better than him. Pivetta is a solid starter (4.06) who they could move, but how do they move him and get a *better* SP back? Bello is their worst starter and he's under long-term contract and is going nowhere. He'll just keep getting the ball and working stuff out. Crawford is steady at 3.59 era, and yeah, you could do better than him, but he's 44th in MLB among qualified starters in era, which means he's a legit #2 starter in all of baseball. I think you could move him for a pitching prospect, but while that may be best for the long term, it won't improve the rotation NOW.
RP: The bullpen could always be improved. Isaiah Campbell needs to get his s**t together. Otherwise, guys are doing well, especially in their roles. Jansen, Slaten, Weissert, Bernardino, Booser, ZKelly, Martin - they've all been good.