This isn't backed by any evidence though. Jay Ritter maintains an extensive amount of data on IPOs here:
https://site.warrington.ufl.edu/ritter/ipo-data/
And his data shows that IPOs for the most part perform about as well as their respective market. That is large multi-billion dollar IPOs perform about as well as the broad market, and smaller IPOs (which constitute the vast majority of IPOs) perform about as well as other small-cap companies.
In other words, investing in IPOs doesn't give much of an advantage or disadvantage compared to investing in other similarly sized companies.
What's true is that most stocks, including IPOs, don't do well in the long run. The half-life of a publicly traded company is something like 10 years.
Also, the OP just does not understand how the market works anyway. Surely if it was obvious that investing in fresh IPOs is a bad move, all of the big boys (banks, hedge funds etc) would short them to the point of equalising anyway. Maybe not to the absolute efficient point, but still, why do people think they can see such a huge obvious trend, and also assume that other people cannot see it?
Banks generally cannot make these kind of directional bets, and the Gamestop saga has shown that it's very risky for short interest to get too high against retail excitement. So if an IPO is heavily overvalued, the level of pressure required to bring it down immediately may not materialize for structural reasons. I made a modest amount of money from SPCX falling, and I'm sure some hedge funds made much more than me, but I and I expect they would have stayed far away if short interest had been higher.