A) inflation b) try to buy a house for 1M in a hcol place. Why would you set the max wealth less than that of a house, something that most humans have been able to own for most of human history, now out of reach for a generation.

You need to realize that absolute numbers are meaningless, they are all relative to costs and inflation. Trying to lock down fiat absolutes is a moving target.

What is a realistic wealth limit for BTC, out of 21M?

Should nobody own more than 1/21Mth the Bitcoin? Less? More?