no one
needs to spend $300k in a year, but unless you are some kind of ascetic monk, you are susceptible to lifestyle creep.
the reason i bring up college expenses (which are about $70k/year at top US schools) is that parents tend to do whatever they can to give their kids the best possible chance in life. even if someone is not purchasing luxuries for themselves, it's not hard to spend tons of money on children. about $600k needs to be set aside if he wants to guarantee that his children can attend any college they can get accepted to. in the meantime, there are plenty of expensive things he can do to improve their chances of admission. maybe this means buying a house in a better school district or paying for private school (possibly >$40k per year per child). maybe it's private SAT prep to boost test score. extracurriculars are also very important for admissions (and are enriching in their own right), and the most impressive ones aren't cheap either. there's always something you can spend more money on to improve life outcomes for your kids.
you can't just say "I have a lot of money, I'm going to spend modestly, and everything will be alright," and have it be so.