This is a myth. Roddenberry issued a memo in 1989 that basically distanced the canon from TAS, but that was because Filmation was going through bankruptcy at the time and Paramount couldn't make use of its shows. But once Roddenberry died, his definitions of canon were no longer binding, and Paramount/CBS resolved the copyright issues ages ago. There have been numerous TAS references in later canon works, like a mention of the Klothos in DS9, the various "Edosian" plants and animals mentioned in ENT, and references to Vulcan's Forge in TNG and ENT. TAS is included equally alongside the other shows on StarTrek.com's reference pages and on Memory Alpha, which limits itself to canonical sources. So there is no reasonable basis for the idea that TAS isn't canon. That was true for a couple of years, but that was decades ago.
True. At this point in time, I do not know how anyone thinks TAS is not canon after so many references in the Berman period of shows.
Not quite. At the time, in the early 1970s, most US animation was still produced in the US. The trend of outsourcing to Asia didn't begin until around 1980, give or take. It was in the '80s that Filmation became the sole animation house still producing its animation in-house -- although they did outsource once, with The New Adventures of Zorro in 1981, because they had too many shows in production that year to do them all themselves. On that one, they outsourced the animation to Tokyo Movie Shinsha, the best animation studio in Japan.
Let's not forget H-B was outsourcing animation to Australia in the early 70s. Series such as the first Super-Friends
(1973) and others from that era were produced down under.