It's not a myth at all. Lots of people are "moveable" these days, not just the super rich.
Because of IR35, around 20 of my IT consultant clients have moved abroad, some to Canada, some to Australia, where they're carrying on doing the same job, for the same UK company, but are now doing the work abroad instead of in the UK. Yes, they may be higher than average earners, but not super-rich by any means.
What about all the doctors who've moved abroad. Tax is part of their decision to leave the UK. Again, not "super" rich, but typically earning 3x/4x the UK average income.
Back in the 70s, virtually all successful authors left the UK because their income was deemed to be "unearned", i.e. passive, which was subject to over 90% income tax!
With many jobs having proved that "working from home" works, then lots of people are clearly able to do their jobs wherever they are located, so moving abroad is no longer a matter of getting a new job abroad if they can simply continue doing their old job.
Lots of major employers are also international these days, so even if you can't do "your job" abroad, many people can simply apply for a transfer to an overseas branch of their international employer.