Imho, this is, objectively, not true (anymore).
Pantasy with GoBricks are superior in coloring and fit; Cobi are excellent for things that should not be taken apart anymore (like tank models); Lumibricks are excellent in fit and have amazing illumination solutions that are lightyears (haha) ahead of lego.
But "should not be taken apart anymore" fits into an entirely different category for me. If you don't need to be able to take them apart any more, it fundamentally changes requirements.
Lego from my youth, which was a hand-me down at the time, doesn't fit well with new lego. So it might be 40 years old, (which seems like a long time until you actually reach that age!)
I think it's more likely do to plastic aging than the original tolerances though.
According to my local news outlet, they’re up 12% in revenue growth in the last year (which outpaces the rest of the toy industry) and up 1,200% since 2004.