In the case of OpenAI you also have interesting tech and a brand that will massively accelerate your career if you want to stay in that field. So while yeah, you have to hire the best people; and OpenAI like everyone else will be paying $LOTS to a few useless engineers in the mix, I think "$900K and everyone knows it" is a pretty good substitute for talent-spotting, which anyway can't be bought.
How do you quantify best? Number of degrees? Publications? Association with prestigious institutions? Past work experience at top companies? Speed of problem solving? All of this is gameable once it starts being _measured_ and enough incentives exist for people to devote their life to winning the "game".
However, if you happen to hire a math olympiad winning PhD with numerous publications from a tier-1 research institution with a known track record in industry, it would be hard to argue they aren't the best. But success breeds success, and top people will keep being poached to other top places. Kinda how money makes more money.
As a concrete example, I've gotten more accolades for silly personal projects that sound impressive, like training a convolutional network to pilot a simulated car on the GPU, than for impactful work at my actual job, which was a lot less challenging.
I guess hiring is just incredibly noisy, and I think companies could really get far hiring less than the best people, and just squeezing good quality work out of them (I believe Amazon is known for this).
Obviously OpenAI should not hire subpar people lol, they should keep doing what works for them, just grumbling loudly here.