I do go to a selective school, I transferred from a comprehensive school start of last year. The teachers are mostly better than my previous school, and go into depth and genuinely want to help students improve. For me the worst part of selective school culture is the fact EVERYONE does tutoring, which can make the environment kind of toxic for those who don't get tutoring (me and a few others). It's also the fact that my school places so much value on people doing well in maths, when it isn't even a mandatory subject. Due to this, a lot of students I know who do amazing in Maths are barely passing in English, which is worrying as English is the only mandatory subject that HAS to go towards your HSC. I don't really have an opinion on whether selective schools should be abolished, but I don't think they need to be seen as the only way to be successful.
Also on the topic of Opportunity Classes, I was in one for years 5 and 6, and it did not do ANYTHING to help me better prepare for high school, we barely did any schoolwork those two years, and I know a lot of people who were in that class with me have struggled with the amount of writing you have to do in high school due to the fact we never had the opportunity to practice and improve our writing. So that's my take.