Where does the idea that engineers cost "a few million" come from? You might pay that much to senior engineering management, big names who can attract other talent, but normal engineers cost much less than a million dollars a year.

OP said "Even if they needed to hire a few thousand engineers at a few million in comp each". That's where the number came from.

Nvidia seems to pay the bulk of their engineers 200k-400k. If the fully loaded cost is 2.2, then it's closer to 440k-880k per engineer. Probably 500k would be a good number to use

they're not hiring 4 engineers, they're hiring a team.

and this isn't just developers, R&D and design are iterative and will require proofing, QA, prototyping -- and that means bodies who can do all of that.