1) If you keep it under your mattress it will be much less than what I described, because every year your nest egg will shrink due to inflation, so you'll just be able to take $25k non-inflation adjusted, which is a big difference from my $25k inflation adjusted (in 60 years, $25k will be $150k at a 3% inflation). My assumption is 0% real growth, not 0% nominal growth, which is what you'd get by keeping it under the mattress.

2) The 4% rule is based on a shorter retirement interval (30 years) than what I'm looking for (60 years). Try to go on firecalc.com and look for the statistical odds of 1M giving you 50k/y for 60 years: the failure rate is higher than the success rate, and that's based on historical data.

3) Yes, my assumptions are very conservative, but I don't believe index funds will return 7% nominal over the next few decades, the world is going to face too many problems in my opinion. That being said, pretty much all I have is invested in index funds despite my opinions (mainly because I wouldn't know where else to invest it, since both cash and bonds are sure losers to inflation), so in the best case I'll be pleasantly surprised.