That contradicts what you said earlier. Apparently Robin doesn't have to be there because she's Luffy's subordinate, but Zoro is still shown even though he's Luffy's subordinate
Robin's role is to help luffy. Her reading poneglyphs is for luffy. The ancient history matters only when Luffy can do something about it. Like The Roger pirates all know the ancient history but it doesn't matter sivce roger wasn't the chosen one so you don't see the Roger pirates listed here.
Zoro became a supernova because he himself had a bounty from his accomplishments. So that alone is enough for people to tell he himself is big deal in the future. Zoro will be WSS and his strength will be his own and this accomplishment will be his own and he will be a top 10 contender in the verse by virtue of his strength.
Get it? Robin's endgame is for Luffy hence her role ends on being Luffy’s subordinate. Zoro being WSS is his endgame and it won't be less of an achievement with or without Luffy