There are no doubt some groups, in both RoSPA and the IAM, that still tend to push the mantra "make progress", but this is very rare nowadays. Most groups expect the candidate to make progress when it is safe to do so, but not to exceed the speed limit, and certainly not to push them to do so until they have picked up all the other skills and are confident, and safe, to do so.
There also some groups whose observers have the arrogant attitude you describe, but they are very few and far between nowadays.
RoSPA and IAM observers are also regularly assessed, particularly National Observers who are assessed by selected local examiners or regional managers.
In fact the IAM have been striving to improve and standardise the observation process and guidance given (or training for want of a better word, though they are not supposed to use this word for fear of upsetting the DVSA). For example, all Local Observers, who were trained and assessed in house, have to become National Observers by April 2025. My group, in particular, have been giving intensive training and guidance to our observers to achieved this.
It is all very well saying that some of your ex-students have gone to advanced groups and crashed, but as you weren't there you can't say for sure why they crashed, or whether they would have crashed at some point in their early riding career even if they were not taking an advanced course. It may well be that their observer was pushing them too hard, all I can say is that it shouldn't happen, no observer should push their associate beyond their capabilities, and I'm fairly sure it doesn't happen in my group.
There are two observers in my group that own their own successful riding schools, they are both happy with the advanced course we run.