I think you have a valid point, although I think it should probably be the "decimillionaire next door" to keep up with inflation and retain its original meaning. This is a case where the floor dropped out and the ceiling is falling, when a "millionaire" doesn't really mean what it meant many years ago.
In 1904, $1M inflation adjusted is $31M now. In 1956, it's $9.9M. Seems to have peeked at 2007/8. The uptick to "billionaire" started around 1982 which is about $2.79M. Words are very discrete bins and usage lag.
While there is a very valid point that many who frequent this site may be considered millionaires and by some, considered wealthy relative to the median in current times, that isn't to say the median hasn't been falling in terms of the sheer scale of wealth these days.
Remember your audience here. You're surrounded by them.