A few points:
1) 100% success in Firecalc for a 30-year retirement is just for 30 years. Increase it to 40 or 45 years and your 'success rate' artificially increases, because it has fewer periods to check against. So you can't somehow magically spend more over a 40-45 year retirement than a 30-year retirement. If you can't spend more, then you obviously must spend either the same or less. And even within a 100% success rate for 30 years, that includes more than just 1 sequence where you end with just a few hundred dollars after year 30. Many retiring in their 30s/40s, or even 50s, want to be able to rest easy for 40-50 straight years knowing that they can enjoy a 40-50 year retirement without any likely problems.
2) It may really be different this time. In all previous times when the interest rates were this absurdly low, equities were yielding 4% OR MORE. The S&P 500 is yielding a paltry sub-2%. In the past, even though bonds were yielding essentially zero you still had good dividends from stocks. That isn't the case currently. This would warrant perhaps more caution on the part of the risk-averse and studious ER-wannabe.