"and lazy/inexperienced/poor instructors who don't jump in and finish/correct the read back and leave ATC to chase it"
I'm tempted to have a go at this, but wont. What I will do is point out that students get 2 goes at the radio call before ill help. If they muck it up once, I let tower correct them and they have another go, if they get it wrong the second time i'll pipe up and complete it properly to avoid holding things up. Everyone has to learn somewhere.
I've dealt with my fair share of trainee controllers too.