I mean, you could consider it cool, I just don't think it's cool. As for the ridiculous factor, what would you think if Jack the ripper was using a cat ear and a buttplug? What if Lu Bu started the fight using street wear punk style with gold chain around his neck?
What I want from the ridiculous factor is Kojiro having stupid ability of foresight, Raiden weird muscle, Qin Shi bubble thing not Tesla using budget techwear.
If Jack the Ripper had a legend about using cat ears or a buttplug: I wouldn't care if he did.
If Lu Bu had a legend about wearing bling: I wouldn't care if he did.
Spartans are legendary for their ability to fight and to die rather than retreating. It's their entire shtick. Their legend is the spear wall, a shield and spear formation. Their legend isn't about tactics, because frankly they aren't very good at them. Their legend isn't about their helmets. It's about being dumb meatheads with shields and spears.
So far Leonidas has the shield, and in the next couple of chapters I'm willing to bet his stupid mace turns into an equally stupid spear.
Plus, getting mad that he might use a mini gun or he's wearing modern fatigues is like getting mad that Qin Shi Huang was naked, Adam knew modern boxing, or the Buddha is a candy eating Japanese street punk. We've been having asynchronous techniques and technology throughout the entire manga. Expecting Leonidas to be any different is silly.