Actually the Ironman and X-men animes were dubbed. In fact they actually had bigger names than the typical anime dubcast in the leading roles of Ironman and Wolverine. Adrian Pascar (who at the time was big from Heroes) first did Ironman there and he became the regular to go to Iron Man VA for the next several years in various productions including Avengers Assemble.
However those were kind of co productions mostly aimed at already existing comic fans. Disc Wars and Future Avengers are aimed at selling the Marvel heroes to Japanese kids who have never really heard of them before, to the point that the actual Avengers are pretty much second fiddle to the original Japanese kid heroes.
They're basically just getting Japanese children ready for the MCU movies when they become older