The original Super-Saiyan

[Fantastische Hure]

I don't know whether to put this in the anime or manga discussion section, but here goes:

The anime had Vegeta talk about Super-Saiyan in the anime and showed an actual visual of a seeming Super-Saiyan. The Super-Saiyan seemed evil and destroyed anyone and everything. Even seemed to destroy the planet that was on, but then the actual Super-Saiyan we see is different.

Now I know this is probably just nonsensical Toei filler, but in-universe why was that? Why was the Super-Saiyan shown in the visual so destructive, where-as the ones that actually appear seem to be able to control themselves.

Both Vegeta and Captain-Ginyu also say that Goku shows mercy so he can't be a Super-Saiyan yet, so what is it? How did this end-up in the legend? Other-wise though the manga lines-up quite well with what's actually shown, only Toei seemed to mess that up.

 

[Captain Cadaver]

Considering the only previous SSJ in canon would be Yamaoshi who was at a low enough level he couldn't even take care of a bunch of likely low and mid class plebs, perhaps he lacked the power to properly control SSJ/SSG. Keeping with that in mind, it's plausible to think that what's shown was the natural result of events becoming embellished or mistranslated through the years, with his lack of control (Ki/stamina) being misinterpreted as a lack of rationality.