"leetcoding" 6 hours and doing "systems design" for 3 hours, totalling 9 hours of heavy cognitive math like work each day while job hunting?

Whev, i'd have an absolute mental breakdown over that. But maybe it's the kids and other responsibilities, how old are you?

I don't even think i grinded that hard in university, i've always only been able to do that kind of work 3-5 hours even when maxing out for an exam, and only for a few days at a time.