I'm one of the more casual anime fans out there, and even I know that there was a "Real Robot" genre was well underway years before Evangelion came around. If anything, I think Evangelion might have been trying to be a subversion of tropes that were already seen as old-fashioned.

Anime "Experts" have no excuse, especially since Wikipedia says that anime like Macross/Robotech were localized in the West and fairly popular by 1985, over a decade earlier.

Not sure why Gundam is being held up as the biggest example, since that's almost certainly what the YouTubers have in mind when they say "all mecha anime." It's the biggest mecha franchise in history and pretty much set the standard of its generation.