I'm not sure if you've misunderstood, so apologies if this is old news. US companies may have teams of engineers in various other countries. But they almost always pay local market rate. In much the same way US companies will pay teams in India their local market rate (which is less again).

My last company paid 2-2.5x a UK salary for a US engineer. Perhaps the ratio for a company like Meta is closer, but I doubt it's equal. For startups you may find random roles that have equal pay globally, but they're relatively uncommon.

Oh, you mean like Spotify? Or those thousands of Mittelstand companies across Europe that Americans don't know about but are actually used in Europe?

But the argument of the parent might be that a very active open source community based in Europe points towards a big potential of experienced developers working at their mid sized companies in the shadow of American big tech. Once big tech is gone...