First of all, we're starting from a point where neither of us know anything about the inner workings of the Sox' FO, or Getz's thoughts. With that in mind, I say that they wanted to send Fletcher down to keep him getting reps and more importantly, away from the record setting parent club. They don't think Colas is ready for a full time audition, yet (the very type of decision making you're calling for), so they activated Ortega.
The fact that they let Horn go means, to me, that they were done with Thompson, and took a flyer on Horn for their troubles. Yes, they knew about Horn. Maybe they tried to sneak him through waivers, or Bannister (who didn't have deep, previous knowledge of Horn) cut bait on him.
This is all a lot of thought, already, for a couple of guys who will get an MLB.com write-up in about 5 years about how they persevered through 5 organizations, and now, they're finally having some success as a long man for a last place club.
I don't see how having a plan, seeing the disastrous consequences of that plan playing out, then trying to adjust on the fly is panicking, or dumping one's plan. Seeing as they had zero (0) rotation pieces entering this season, and imagining the restraints on payroll Getz was dealt, he and Bannister worked out a plan to identify guys who are rehabbing, or trying to rediscover recent success, put a more competent defense behind them, give them a good game-calling catcher, and run with that, giving the prospects more time to develop.
They're still running with Crochet, Fedde, and Flexen. Soroka got the Flexen treatment. Clevinger and Keller are innings. They tried Nastrini and Cannon, maybe even to discover what non-prospect hitters at AAA couldn't expose, and now they're working on their games. I don't see this as some huge divergence. If they traded Nastrini and Cannon for guys who could cover 5+ innings, that would be panic.
Add to that, 3 starters went down with injury, and another 5 started out in extended catastrophic slump. I think if Chris Getz could predict batting slumps and injuries, he wouldn't be a GM. He'd be sitting on a mountain in Tibet, giving life advice to those who could reach him.