The Superhero Database Classification number, or SHDB Class, is a number that represents the overall 'power' of a character. All traits of a character are used for calculating the Classification.
What it DOESN'T mean
This doesn't mean that a higher class would always beat a lower class character. But the bigger the difference in Class is, the more obvious it is who'll win in a fight.
How is this calculated
( INT^1.3 + (STR*0.5 )^2 + (SPE*0.5)^2 + DUR^1.6 + (POW + (SPS*SPL))^2 + COM^1.8 ) ^ TIER
Super Power Score and Level
Every Super Power has a score (SPS) that is used to calculate the Class. Each Super Power also has 3 levels (SPL). The level is set when connecting that Super Power to a character. The level determines the final score, of the Super Power, being used in the calculation.
(1) Main antagonist at one point tanked being struck with an artificial Black Hole. This could potentially scale the durability of Main antagonist to Planet Level, since even the smallest Black Holes in nature (even when they're smaller than 1 inch) tend to have at least that sort of Planet+ Attack Potency casually.
Considering Ikki eventually fought and defated the main antagonist in an epic (physical) battle, especially when Ikki became the Sky King and absorbed all of the gravity and all of electrictiy of the entire planet, Ikki could be scaled to Planet Level, too.
However. Both of those aforementioned (possible) scalings could easily be seen as Outliers, too, because the most average feats of most characters in the verse can rarely be calced as more than only ~ Town Level (7-C).
So, depending on how you wanna interpret the high end feats (Black Hole, Sky King with all Gravity), Tier 5 (Planet) can be acceptable, but if these are outliers, then Tier 7 (Town / City).