Your example of the retiree with 1mm calculates to be a 3.3% COLA between 65 and 80. That's average inflation. So?
Well considering how far above equivalent annuity rates we expect to start at, also having "only" a >3% growth even in the early years, seems a pretty good deal to us.
The reality is that this is all that the math allows without increasing risk.
Clearly if we have some stellar years returnwise, this would also add a few bps on top but this will be spread out over the longer term.