The "Millionaire's Next Door" in that book were working in an environment different than the current, that's a fact. Now whether the current environment is "less honest and merit-based" (as I happen to believe), or not, it is certainly different.
Bubbles come and go, some are long, some are short, some are consequential, some are not. For example, real estate bubbles: these are most dangerous because it is usually the most substantial asset purchase an individual ever makes, and it is typically 90% leverage. If you fall ass-backwards into the right spot on the development curve, you can literally turn $50k (down payment) into a million++ dollars - if you guess wrong, you're bankrupt and you pray that you have a non-recourse loan.
Bubbles come and go, some are long, some are short, some are consequential, some are not. For example, real estate bubbles: these are most dangerous because it is usually the most substantial asset purchase an individual ever makes, and it is typically 90% leverage. If you fall ass-backwards into the right spot on the development curve, you can literally turn $50k (down payment) into a million++ dollars - if you guess wrong, you're bankrupt and you pray that you have a non-recourse loan.