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.
Thanos loses to Cull and Proxima, Proxima who was being defeated by Falcon and Cull who was being defeated by an inexperienced Hulkbuster pilot tripping all over the place. If Cull's skill was so low compared to Thanos it means his strength would have to be much higher, and we all know that Cull is pretty weak after seeing him smeared like a bug on Wakanda's windshield and stepped on like a roach by Scott.