On top of that, Harlock does all this without any supernatural powers, unlike Ryu, who has to rely on being half dragon, or something like that..
WTF?!? "A clan of ninja that has spiritual, physical, and magical ties to ancient Dragons" doesn't mean he's part dragon otherwise he'd look like a reptile in humanoid form that could fly and breathe fire. From there, you clearly don't know what you're talking about.
Quote from Ninja Gaiden wiki
As a ninja Ryu is in perfect physical condition though he has quite a muscular built, this does not render his outstanding speed and agility which allows him to perform the most complex of aerial acrobatics and while being in such built he is so strong that he is capable of wielding the most enormous of weapons and still being able to perform amazingly fast swings.
It could be considered that he's is able to maneuver in such a manner for the fact that he is a descendant of the Dragon Warriors, however Ryu doesn't appear to care much about his inherited super strength and only considers that he is strong for his training, as he explained to Rachel.
Harlock destroys the entire Mazone fleet with guns from his ship, the arcadia, as well as his laser pistol. Harlock's reflexes are at least equal to that of a ninja's.
Fighting an entire species of female-looking aliens is tough, due to their looks. The mazone are actually asexual, and thus a female body suits them more for taking over the world. It's easy to fight monsters and men, but much harder to fight someone you are attracted to. Why else are the best villains women?
All heroes save the world in some way. Ryu simply saved it from a war which would cause massive destruction across the planet. Earth would survive pretty well. That leaves saving the world from mythical creatures. How many did he face? Surely not as many Mazone as Harlock. There was no chance for Earth to survive had Harlock not saved them (politicians would rather play golf than defend the Earth. It's a lot like futurama and zap brannigan).
The only thing I could see which could rival space pirates would be space ninjas, but even then, most of their "ninjability" is lost in space, isn't it? However, introducing "space" is cheap and shouldn't be used in the classic debate.
Including soldiers in the ninja category is ridiculous, not to mention unfair to the debate. Jack Bauer can't die, for one, Chuck Norris is Chuck Norris, and Jason Bourne is a $30 million psychopathic killer. An assassin isn't necessarily a ninja. A ninja is an assassin. There is a distinct difference in being a soldier and a mercenary. Ninjas are mercenaries, not soldiers.
You're telling me that fighting beautiful women is difficult? That sounds so dumb. There are boss fights where they are females, and Ryu Hayabusa fights them. You're trying to consider that males will have a tough time attacking females based on looks? In real life, whether beautiful or not, either gender can get raped or killed regardless of how sexy looking they are. if a beautiful woman is trying to kill you and/or the entire planet, and you know it, how the hell does appearance stop you from attacking them? Queen Marie Antoinette of France had her head cut off and the people who wanted her and King Louis XVI dead didn't really care about her looks. Queen Brunhilda of Austrasia was torn apart where each limb was connected to a horse.
You're saying "Space", right? In reality, one tiny scrap metal can demolish a space ship (Ever recall the close call International Space Station incident?) if you're considering "ninjability" is lost in space. In words, ninjas can adapt the harshest existence in reality and fiction, and they too can adapt outer space.
So you're saying Ninjas are not soldiers? Sam Fisher is a soldier and through dialogue, non-playable characters had considered him as a ninja. If the latest Splinter Cell game had connected his fighting style, and other Splinter Cells, to Jack Bauer, Jason Bourne, James Bond, and Chuck Norris, then they are ninjas too. A ninja like Sam Fisher can bypass guards like a ghost, doesn't have to kill or knock them out, and therefore can complete his missions to prevent enormous catastrophes without getting detected.
None.