Some of my most mediocre acquaintances have jobs at FAANG/Big N. You don't have to be exceptional to land a high comp job there, you just have to be exceptionally tolerant to BS and mindnumbingly boring work and be willing to grind interview prep.
If anything, landing a job at an unicorn is much harder cause they care about things like culture fit, enthusiasm, esoteric FotM frameworks, and entrepreneurial spirit.
Trading one anecdote for another: I've met plenty of mediocre engineers at unicorns. Every company has its own flavor of BS and "mindnumbingly boring work."
My company isn't well known and the 200 or so engineers who work here have an average all-inclusive compensation north of $200k (many see above $225k).