I did School Direct and the trainee year was brutal! I had no sick days, taught 17 then 21 lessons a week and worked at least some of every day until a couple of days into the May half term, when I handed in another bit of coursework.
Teaching gets easier in the ECT years and every year after that, especially if he stays in the same school for a few years. Even though he'll be teaching more hours, he can focus on teaching rather than having all the coursework and classwork to complete.
He should speak to his mentor, especially about the amount he's planning. Can his mentor or department give him old lesson resources he can adapt?
He is over the peak of the year - summer might involve more marking (depends on the programme he's doing) but if he can make it to next year, everyone I know found it more enjoyable and easier.
I'd also recommend he try organising a placement in a different school and try to do his ECT years not in a large academy trust. Or at least be prepared to interview at and move to another school before leaving teaching, it's what stopped me leaving the profession.
Edit: if he's in a STEM subject he should have his pick of schools!