So, I would really hold back on worrying about a lot of the things you're pointing out here. First, the walks; in his first start, two of his three walks came in the fourth inning during a downpour. He could barely hold on the ball. In his second start, two of his three walks came on the first two hitter and on nine pitches. It was very cold that nigh, once again, really felt like he was struggling for grip, not command. Should we entirely ignore them? Probably not, but I think both are easily explained away by weather and rust more so than any concern.
Secondly, his BABIP is low. And yes, the LOB% is high. But here is his statcast page:
The only issue on there, really, are the walks. He's absolutely elite in most categories. So if we can explain the walks and he's crushing it in terms of whiff, zone contact and hard hit it's not shocking that he's giving up a low BABIP. When we look at MiLB BABIP we have to look at it a little differently than MLB data - sometimes, when we see low pitcher BABIP, it's not that it's luck, it's that his skill is so much better than he's dominating hitters. From watch his his starts, when he's not walking guys, he's dominating them in zone. It's also why the LOB% is high - guys aren't getting on base often. And when they do, they can't string hits together. It's a one and done. He won't keep a 1 ERA or the 94% LOB%, but I also don't think they're numbers to worry about, if that makes sense?
As well, his stuff+ is glistening. His third pitch is grading out as a good stuff+ offering.
I really don't think he's very far away from being MLB ready or an upgrade for the rotation. Colin Rea has been much better than expected, but I'm not going to fully say he's that good yet. He's throwing a completely different pitch mix so far (scrapped the sinker for a four seam) and the league hasn't had a chance to adjust.
I wouldn't bring him up today; I think two maybe three more goes (and they're similar to the last two) and yeah, he's probably MLB ready. And yeah, I do think he's going to be an upgrade in the rotation over either Ben Brown (who still waffles from control issues to impressive) or Colin Rea (who I am not exactly sure what we have yet). No shade on either, I really think that highly of Cade.
To put it this way; on a pure RPM basis, his slider and curve are grading out on par with Dylan Cease as is his fastball velocity. And unlike Cease, who's struggled with command consistency throughout his career, Horton tends to pile up the strikes. The upside on Horton is basically "What if Dylan Cease dogpiled strikes?"