@.access:
I think with time people get used to some designs and don't realize what those characters really look like. It's not just Marco, but also Shanks, Teach, even Luffy, all of them look like complete background fodder characters. Damn, Roger is probably the biggest offender and he is the Pirate King. Even Big Mom, despite an interesting design, gives zero "strong character".
Of all the big named pirates, Kaido and the late WB are the only ones that look properly badass in the way we are used to, you look at them and you know they are strong. But all the others? You wouldn't even bother looking at them in any other manga… and that's one of the best things about One Piece.
I think it's moreso that almost all of those designs you mentioned appeared in the beginning of the manga. Where the creative standards for One Piece were a lot more simplistic. They work because they had a lot less surreality to contend with and have major plot beats associated with their characters since the manga's early days. As well as a fair bit of nostalgia. So while I wouldn't normally think any of the designs you named are "badass", calling them complete background fodder characters is too harsh. When Oda makes background fodder characters, they REALLY look like background fodder characters. You can't tell me the guys you mentioned look as forgettable as the guy who was calling out the Revolutionaries' names. Luffy, Shanks, Marco, and Roger have JUST enough colors, attire, details, quirkiness and thematic connotations poured into them that they at least look like main supporting characters in any average manga. And Luffy himself is probably meant to look so simplistic in the first place so that he is relatable, iconic, and maintains his charismatic underdog status. They are very simple designs, but still effective and memorable.
And I don't know about you, but I would totally find Big Mom's appearance intimidating in any manga. Particularly in a kooky Joker way. The dress is very simple, but her other clothes, size, face, expressions, and powers are as One Piece as you can get. The same goes for characters like Ivankov. They aren't "badass", but they're silly and crazy looking enough for me to know they're BIG NEWS I shouldn't underplay.
These Revolutionary designs are just as fine in their own right too. The tech guy and the giant technically have more quirky effort put into them than any of the designs you mentioned. They could easily be minions for a main arc antagonist in terms of design intricacies. But that's why they give me a Hunter x Hunter Shadow Dragons vibe where I can easily see all of them except maybe Karasu getting obliterated to hype up somebody else invading the Reverie. They're detailed, but the things chosen for how they are designed (aside from plague doctor crow guy) give me a "these guys are supposed to look tough but I bet they're really scrubs when it counts". They only look like they are designed as jokes that aren't particularly simple/weak but also don't look that cool, creative, or intimidating like Ivankov and Big Mom. They're sort of in-between. That mediocre middle where the author doesn't really put their heart into these designs for them to significantly stand out or communicate that much besides one or two things.
Meanwhile, I look at Luffy/Roger/Marco/Shanks and I get a "this guy looks totally goofy/weak, but it's because of that I know they're going to shock my expectations somehow". A lot of this is thanks to, again, what time of the manga these characters were introduced. The Revolutionary commanders could have easily been the main characters of One Piece if this chapter was the first chapter of the series in some alternate universe. But it isn't. And story context does affect the impressions designs have on us, which is fine.
Except the whole idea here was the RA not taking care of anyone. They only provided support, the ones doing the actual fight and taking the pirates were the citizens. Their intention is not for people to depend on them to be protected in the place of the Marines, to be ruled by them in the place of their kings, but to rally people by providing motivation/means/support so the people can trust their own power.
This is very typical for Oda. It reminds me of when Ivankov said he wasn't a miracle worker and that miracles only happen if you work for them. Luffy needed to endure the pain for the treatment to work and got encouragement form Bon Clay and the others on the side.