H1B holders are free to change employers, but the new employer has to apply for a new visa (not subject to the cap). I've changed my job 3 times on an H1B, always for a better role and more pay.
Theoretically, nothing prevents them from changing jobs just like with a <6 y.o. H1B. Also, theoretically, nothing prevents the old employer from recalling the I-140. In such a case there are, probably, ways to still retain legal status but they are far more complicated than filing for a new H1B.
Also untrue. Employers can only revoke I-140s within the first 6 months after approval. After that, they can't do anything if the employee decides to leave.
The challenge with finding out whether the process was working before is inherently difficult is what I think. Whom is it working for? And for whom it isn't? Again I could be wrong
How does it apply to tech?
Upon review, it's apparent that the 'visa for people with skills that the American market doesn't have' argument doesn't fly - the requirements only establish that the visa holder be competitive with Americans. You might be thinking of the 'extraordinary ability' category of visas, which are O-series (instead of the H-series of H-1Bs).
I'm also unclear on your criticism of consultancies - there's no criteria for the job to be STEM in nature, and I don't think it's an extraordinary view to hold that other fields may be technical/specialized. Fundamentally, very very few employees are irreplaceable (for good reason) by someone with sufficient motivation/training.
In defense of H-1 visa holders (especially fresh grads), I'd argue that if you outcompete locals (on even salary conditions) through fairly rigorous recruitment processes, overcoming the lack of local network and cultural/language barriers and survive the lottery cull, then the position has been earned. [1].
Finally, your argument about 'having the time to gauge applications' is absurd. Either the process was working before, or it wasn't. If the program was compliant prior, then extending processing times is fundamentally a violation of due process, and effectively re-interpreting existing law.
[0] https://www.uscis.gov/working-united-states/temporary-worker... [1] Fair disclosure, this was my path