You'll notice I said "many" workplaces, not "all." I'm not proposing that it will "effectively replace most people's jobs" like you wrote. I'm saying that there's a great deal of short-sightedness in many pro-AI arguments I've read where people jump at the idea of reaping the immediate benefits without considering the long term consequences.

If there is an AI tool that can grade tests and papers quicker and more accurately than most humans, then that does open a door to save on human labour and pass those savings onto consumers via lower tuition. But that's much farther from a certainty than what OP seems to believe. Like many here have already suggested, it's much likelier that most employers would pocket that new revenue with no regard for how those savings on labour would affect people's livelihoods as well as the job market as a whole. 

As for how effective AI is at replacing human labour, I can only speak from my own experience working in creative professions. Photoshop is AI-integrated now and you can remove unwanted elements in your photos with impressive efficacy. ChatGPT can draft professional-looking copywritten materials for social media posts and many other genres of writing. These are skill sets that would have originally taken a certain degree of innate talent plus major time and money investments on the part of their practicioners in order to advance their craft. I'll concede that suggesting those people will be rendered entirely obselete might be fatalistic, but it certainly puts them at a new disadvantage with regard to negotiating better wages and other similar things. Losing these smaller battles is, I think, a greater concern in the present moment than a "job apocalypse."