I disagree. Making a pitcher change his approach IS a MAJOR change. It is why a guy like J.A Happ can go from meh underachievier to looking like Barry Zito in his prime in a few weeks. Imagine changing how you approach pitching can lead to that much success in the short-term imagine long-term consequences if the the coach messes him
Happ had success because Searage told him his most successful outings came early in his career when he was pitching from the opposite side of the rubber and told him to stop throwing his curveball and lean on the fastball more. Those aren't exactly major changes. What the Rays did to Glasnow (changed his entire windup) and the Astros did to Morton and Cole (let them ditch pitches they weren't comfortable with, pitch off an elevated fastball, and use their out pitch more- Cole's slider and Morton's curve) were major changes. Searage could probably benefit more from trying out some major changes with certain pitchers. For example changing pitch grips, glove position in the windup, etc would be major changes. Telling someone to move to the 3rd base side of the rubber and throw more fastballs is as minor a change as you can get.
Searage's approach has always been:
Step 1: Look at video of the pitcher's most successful stretch
Step 2: See what has changed in the mechanics/setup since then
Step 3: Keep tweaking until desired results are achieved
Those kinds of changes are relatively small because their minds and bodies already have that muscle memory, they've just gotten away from it.
That's why his successes have entirely been with veteran pitchers with spotty track records. Not a single young pitcher has had any sustained success under Searage and I firmly believe it's because of his approach of small tweaks based on prior successes; young pitchers have no such video for Ray to dissect and tweak back to.
I also think he is put behind the 8-ball some due to the way the Pirates develop, or more accurately, fail to develop, their pitchers in terms of developing pitches early in their minor league careers and advanced pitch sequencing in the higher levels of the minors. Those two things have hurt a lot of the pitchers coming up to the big club and, as someone stated earlier in the thread, is a big reason why Glasnow and Keller didn't have immediate success, especially on the secondary pitch development side.
This is also seen from interviews with Shane Baz:
"Almost immediately, the Rays were more -- I don't want to talk bad about the Pirates -- just completely different, honestly," Baz said. "It was a whole new perspective, a new approach to pitching. I saw pretty quickly that I would be big in spin rate and that stuff. They told me my fastball would have the top spin rate in the majors, if I was pitching there right now. I don't have to be right at the knees every time because the movement is going to be so good, guys aren't going to hit the fastball anyway. The slider is so hard, too, that it's going to be a good pitch as long as the arm slot is the same. The same with my curve and change. That was the first thing they showed me, and when I saw it in action, I just thought, 'OK, great.' Instructs (rookie ball) was a good little trial run, and I've carried that into this year."