There is no country with objectively cooler characters or themes. What you're doing here is claiming that there are several different awesomely crazy random legit extreme to the max things that the best and brightest of Japan have to offer, and America just has 'guys with guns and gruff, low voices who don't do much cool stuff.'
now I will list off why what you said is cool, isn't always cool.
Giant robots aren't always cool, see Jet Jaguar.
"Plantet-Buster characters" are rarely cool, it's often boring to see one character who can just do anything he/she wants, and to know that they can't lose. See Ichigo from bleach.
Crazy hair and outfits are defiantly not cool. It's over the top and gaudy. See yugi moto
And having swords and guns doesn't instantly make something cooler. Not to mention that everyone uses swords and guns in their fiction. But I guess you're emphasizing on the 'over the top' aspect. Well to that I say that subtlety subdued actions are often cooler than epic gnarlyiness brah. I believe that the 'say what again' scene from pulp fiction is much cooler than oh say ichigo vs rukias brother ( sorry for picking on bleach so much).
But none of those traits are exclusive to Japan or America, so try not to think like they are.
And your examples could easily be flipped around.
Why does America have such cooler characters? We have guys like the man with no name, Jack Burton, Travis Bickle, Ellen Ripley, The Bride(kill bill), Robo cop. They're all super awesome with they're take no shit attitude, wise cracks, craziness, Robot suits, epic killing swordfightingness, and all japan has are emo highschoolers who smirk and and dance.
See Japan looks stupid there. Actually I look stupid there, but that's the point. Cool is subjective, and cool is from all over the world. Except Whales. HAHAAHA