As I learned on a recent trip to watch a game in Altoona, the players who are there are there for a reason. They've got to get A LOT better before they're competent major leaguers (at least the ones I saw).
First, I'll start with Omar Cruz. I saw his worst outing of the season against a good Somerset lineup. He's got a good breaking ball, but is a soft-tossing lefty. I heard many violent collisions between bat and ball when he was pitching. The most disappointing being a gap-shot on an 0-2 pitch that was center cut. I'd bet things like that are keeping him at AA.
Then there's Mason Martin. One well-struck double to the opposite field to go along with 3 terrible strikeouts and some defensive miscues. There is a lot of hype on this site and others about him. I'm not even remotely convinced he'll ever be a bench player, let alone an MLB first baseman. His swing was as big and long as the Horseshoe Curve.
Ji-Hwan Bae and Cal Mitchell looked marginal, there is still a ways to go for both IMO. Not as bad as Martin, but not great.
Now for the good: the ball jumped off the bats of Diego Castillo and Jack Suwinski. In Suwinski's case, his stat line didn't show how hard he was hitting the ball. It sounded different off their bats than the others. Matt Fraizer also looked (and sounded) pretty good in his ABs. I'd say that Suwinski was the best of the three, but that's just based on what I saw.
There are guys like Connor Kaiser and Garrett Koch still getting ABs in AA. I get organizational depth, etc., but with Indy littered with AAAA players, why not promote a few guys to open up spots for the worthy ones from Greensboro?