If you need someone in the same time zone who speaks English at a level that enables them to contribute work of the same quality and volume as a native speaker, you've really only added Canada.
If you discount the language requirement, you can add Central and South America.
Only if you discount both the language requirement and the time zone requirement can you add the rest of the world.
Time zone issues are a bit of a pain, but manageable. As long as you don't have to meet with them daily, you (or they) simply schedule the once-every-week-or-two-weeks meeting at a time that can work (a little earlier in the morning or later in the evening). It was quite customary to leave early or start late on some days to make up for having a 1-2 hour meeting in the evening or early morning. This is well understood.
To be clear: Those developers were "first class" employees - treated similarly to the ones in the US.
[1] Indeed, although their accents may have been difficult to follow, the reality is they understand a wider variety of accents than do most Americans, and so Americans complaining about their accent would be viewed as petulant.
Few good companies do things "based on price alone" That reasoning will not get you far.
Having said that, I did interview with an SV startup where probably over 50% of the employees were not in SV, so it may become the general trend.
Yes, everyone should learn about negotiation. And as the authors of Negotiation Genius point out, you're making the mistake most people make - only considering your BATNA and not considering the other party's BATNA.
Ask yourself what alternative Facebook has if you insist on a Bay Area salary while living in the Midwest. The answer will be "More than they had pre-COVID." This reduces your bargaining power. Allowing remote work has significantly increased their pool of applicants. For every one of you, there are probably over 10 people as good as you who are happy taking a 20-30% salary increase while still getting paid 30% less than SV folks.
While your advice is sound, you are only providing one half of the dynamic. One of the lessons in almost all negotiation books is to spend time understanding the position of the other side.