Not all of them fought the F6 though. And like I said he was talking about the alliance yet if we are to powerscale such statements, what about Law and Kidd etc who were not called muscles, stars etc.
He's probably calling them the stars because they are the only ones there in fighting shape
Technically they did, Big Mom intervened of course, but that´s not something Marco is gonna predict.
Marco won´t know everyone in the alliance, he is talking about the Strawhats, hence why he says "Strawhats, you are the real muscle, what you doing here", later he further clarifies by saying "you guys are not meant to be fighting these no-names", meaning Marco is pushing the narrative of Strawhats matching and becoming a Yonkou crew, and actively is trying to create the scenario of Strawhats fighting Beast Pirates (ch 997-998), hence why he is stopping Big Mom and her crew from intervening, he is carrying Zoro to the roof, he holds Queen so that Chopper can smack him.
And why? Well, that would take a longer post, short version, Strawhats are carrying Ace´s will, hence why he thinks of Ace while he is carrying Zoro to the roof and we get the small flashback, dude was literally crying (also some Marineford stuff of course, considering Luffy is the one the entire WB Pirates tried to protect).
This got an interruption when the Samurai were all infected, and Chopper needed to find an antidote, hence he occupied King and Queen for a short while and prevented them from attacking the Samurai and Chopper.
And in that context, Marco seeing the Strawhats as Yonkou main crew, i understand the statement of rising stars, the new generation, who match the all-stars of Beast Pirates, so basically seeing Zoro and Sanji as the Strawhat equivalent of commanders, basically matching their respective counter-parts.
Now, one thing you are right with, i don´t think Marco knows Jinbe joined, so there´s that, but Jinbe is also hardly from the new generation, and is already a big name who does not have to prove anything and make his name known. So if you want to push it, sure Marco does not know Jinbe is there, but that does not detract from Marco seeing Sanji and Zoro as the respective commander and all star of Strawhats.