I'm not saying the right call is 100% t-bonds, but when you say things like "Over something like 30 years, the only question is whether your investment will outperform inflation or massively outperform it", you're making guarantees based on data from a narrow slice of history that is also the most economically favorable period just about ever.
Equities are the residual claim on assets, and their outperformance is predicated on growth. Economic growth comes from growing population and productivity. Neither of those is a given.
And in part it's precisely because of the worst case scenario happens where worldwide stocks don't outperform treasury bonds, you're likely living in a world where your money isn't legal tender anymore anyway, and any stock/bond investment decision you ever made basically irrelevant.
So if decisions regarding the extreme downside risk are irrelevant, you might as well optimize for the upside.
For broad-market equity indexes, this point is at roughly 140% stocks / -40% cash. So it's not close to being an issue with current market expectations for a 100% equity portfolio, but generally speaking there is a level beyond which you cannot further optimize for upside at the expense of downside.