The reason that Keita and everyone else in Akumasu are un-heroic is because the Heroic people are helping 3G fight the Zonders.Since Betterman and GaoGaiGar have a Shared Universe, the reason why the Story of Betterman is mostly casted by a bunch of un-heroic individuals is because all the heroic ones are too fired up about helping GGG with the Zondarians/Primevals/Sol Masters at the time. Thus the only person on the earth who is "heroic" is Betterman itself. I would further theorize that Betterman takes place either during the events of The Battle of Jupiter from the GaoGaiGar TV series, or during the events of GaoGaiGar FINAL. since that would mean that most of the heroic people would be far from Earth at the time, allowing Algernon to capitalise on the fearful masses. Going by the Project Z trailer, what was left of Akumasu and 3G (after the aftermath of Betterman's and GGG FINAL's respective bleak endings.) would need each other to survive, thus facilitating the mixture of Kakuseijin and Mechanoid tech to create Gai Go and Gao Gai Go, and for Mamoru and Kaido to arise as the world's new heroes, even if they are still just children.
Betterman (and by extension GaoGaiGar) share a universe with Nasu's works, Tsukihime and Fate Stay/Night.During the Warp Mode HQ infiltration, Mamon reveals that everything was going to plan, just as the Akashic records - the Spiral, or Root of the World - had fortold; that the Best Man would appear, and that the Betterman would face him. To that end, Betterman shares some startling similarities in his duties and goals to Counter Guardians, but cannot be a counter guardian himself, as he still possesses his own will. Perhaps, then, he is not subservient to Alaya, the consciousness of humanity, but to Gaia, the consciousness of the planet...?