This can't be a to-die-on rule though. Retail would've never bought GOOG, or TSLA, or AAPL if that were the case. Maybe I'm just being pedantic.
Even for good assets there's a price you shouldn't pay. People are joking(?) about triple-layer SPVs where you can get pre-IPO exposure but at higher-than-IPO price.
Google and Apple didn't go through ten funding rounds like today's startups do. Apple had one angel and three rounds, Google had one angel and literally just an A round after that; then retail investors could capture all the upside. Now there's way more time for private investors to pick the bones clean before it gets dumped on the public.
I think you're both right. Those were great opportunities, but the proportion of such opportunities which are made available to retail traders has greatly diminished over time.
There's a great chart out there somewhere (I couldn't find it) which breaks down the impact of private equity on the availability of such opportunities in public markets. It showed a dozen or so companies (like Google, Apple, Uber, Stripe, etc) and broke down their market cap gains into two parts, "pre IPO" and "post IPO" gains. Of course, the pre-IPO gains were only available to private equity (or, at best, accredited investors), whereas the post-IPO gains were available to retail traders as well.
"Older" companies like GOOG & AAPL were much more likely to have experienced that vast majority of gains after their IPOs, meaning retail investors could have made big money by betting on them early. Meanwhile newer companies (like Facebook, Uber, Stripe, etc) were much more likely to have yielded the vast majority of their gains before their IPOs, meaning retail investors didn't have the opportunity to benefit from big returns.
Survivorship bias and the corporate finance world of today is completely unrecognizable from the world of Google and Apple. Just look at the resulting performance of the SPAC craze