It's a fair question, but it brings up two or three questions that are equally important.

• Sabo being a Celestial Dragon is likely a huge talking point for a political group like that. To the point where I could see Dragon prop him up, even if he actually has no further value.
• Even if Sabo wasn't always number two, you have to imagine the messaging that he was a Celestial Dragon would make him noteworthy in the organization. Like, if you look at politics, he might not be the President or even Vice President, but there are certain notable people who stand out for one reason or another.
• In the event none of this is really true, it would still take an action to make him go from one level to another. This could've taken place between the time skip, but it's the type of thing that could've been portrayed better.