"The majority of startup companies will end up losing money" is a tautology: true no matter what the inputs are.

A bubble is when investors are making lots of money off other investors by trading stuff that isn't worth anything. Risk is being grossly and broadly mis-assessed (deliberately or inadvertently). The bubble pops when people realize this.

In that sense, "majority of startup companies will end up losing money" is actually not a bubbly thing at all. Bubble mentality would be "most startup companies will IPO for huge valuations within a few years."