I wouldn't say slow learners are typically the problem. From my experience in teaching it's the students with lazy habits that tend to break down the professors' effectiveness. People that refuse to "learn how to learn" and expect everything to be googled for them can be difficult to filter for during the interview process and really cause a drag on the class as a whole.
I think that's very much a thing. I do think that some folks ... just can't beyond that, but I agree lazy habits are the worst and frustrating.
I put in a TON of time outside class when I went to a bootcamp. I'd make progress and come back with a quick question for the instructor, and there would be a series of people with the same questions waiting to talk to the instructor who clearly did nothing since the last time they talked to the instructor and were asking the same question as the day before who are mildly perturbed the instructor doesn't just give them the answer...
A lot of the time I just gave up trying to talk to the instructor.
