It is most definitely NOT a myth. I made a thread a while ago about how desperate I was because no matter how hard I tried, I just could not get ANY of my 4 amiibo-summoned villagers ping me to move out.
I time travelled back and forth all the time just to cycle through villager pings for almost 4 days straight, gathering more than 100 pings total, and NONE of them were from amiibo villagers. This includes both cards and splatoon amiibo-figures. I had to completely give up on getting the rest of my dreamies and I had to register my final dream adress for that town with about 4 villagers I didn't really want but got stuck with.
Now I know that apparently many people have had no problem at all with moving them out, but that definitely wasn't the case for me. And there is absolutely no way it was just bad luck. 100+ tries to no avail means that something in my game was set in stone about making those villagers stay no matter what. The only explanation I can come up with is that some players (including me) must've unknowingly triggered some sort of requisite, mechanic or bug that makes their game act that way.
Personally I'm now too scared to ever summon directly amiibo villagers again. I don't want to ruin yet another save file because of this madness. I used to be really eager to expand my collection to invite whoever I wanted, but now my cards and e-reader could just burn for all I care. No way I'm ever cursing another town with permanent villagers.