I think I was really lucky with my mentor in my first placement (going to Phase B school for the first time on Monday so will see how that goes!) so don't recognise your cycle of "plan, get criticised, teach, get criticised, evaluate, repeat". My experience has been more along the lines of "plan, teach, get encouragement with tips of how to improve, do a quick evaluation form when I get time, repeat". Still time consuming, but less demoralising!
It certainly has been a lot of work - teachers in my first placement department were very helpful but worked quite independently, all producing their own resouces, and the expectation was for me to do the same most of the time. So with starter worksheets, reading activities, games, powerpoints, grids for speaking tasks, etc. on top of planning the lesson structure itself, it was an awful lot of work, but I enjoyed
teaching the lessons and my mentor was supportive.
Do you have a visit from the university to moderate your mentor? In ours, the university tutor observes the lesson, then before making any comments of their own, they observe the mentor giving feedback. That way they can check that the feedback is constructive, rather than either ripping you to shreds or just saying it was great and not giving suggestions for improvement. If your mentor isn't fulfilling the role properly, this is something you should discuss with your co-ordinator or university tutor.
It seems like the main things you have a problem with are the constant scrutiny of being observed, and the amount of time it takes to plan. Both of these (I am assured!) will get better.
As an NQT you have to be observed a minimum of once per half-term - 6 times in the year. Even if it's more than that (due to needing extra help, Ofsted, faculty review by SLT, etc.) it's still going to be less than now, so you'll have more independence in the classroom. And after the NQT year observations are even less frequent.
In terms of time, at the moment I find it hard to imagine how teachers plan 20-something lessons per week and still have free time, but they
do, so I trust we'll get there too. All of the teachers I know work bloody hard, but they definitely have a lot more free time than I found I had on placement and I was often jealous hearing them talk about doing normal fun things after they'd finished their work. I suppose it partly gets quicker because of being observed less, as I know observation makes me overthink things. Also after the first few years we'll have a bank of resources we can reuse and adapt rather than making everything from scratch.
If you do decide to continue and apply for jobs, since you teach a shortage subject, hopefully you can be a bit more choosy about where you apply, and things like the level of scrutiny (whether you have to submit lesson plans to your NQT mentor, for example) would be something to try and find out about.
If you really are completely "disillusioned with the teaching profession" then by all means, get out now - it's not worth causing yourself stress if you really don't want to teach. But if it's those 2 issues (rather than teaching itself) that you have a problem with, it might be worth sticking it out and seeing if things get better.
Good luck whatever you decide.