Hmmmm very few would be my answer. Believe it or not, i know a good few of those english language school owners/managers. I know they used to lobby for visas a fair bit from my time in china. There were some schools that had reps as visa factories where barely any of the students came in at all. Others were quite conscientious about it.
Half and half I’d say, they do want to learn English but want and need to work.
I would be of the opinion that even when they are playing within the rules they are visa factories
A mate worked in a school in Galway for years. There’s some process by which you need a Garda to evidence some paperwork for a six month extension. He said it was well known among the students the girls could call out to x Garda in a station in county Galway and have whatever they wanted signed for a price.
Very few do in my experience (a small minority do need certification to get certain professional work) but the vast majority use it just to get in and work (which I’ve absolutely no issue with). I’d much rather then just applied for a working holiday and didn’t have to shell out for a pretend course.