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.
2. That was the first time when sasuke awakened susanoo. That's why at that time he had no idea how to use susanoo. Also that was a half skeleton susanoo. Don't compare it with itachi's susanoo. Itachi's susanoo. Itach's susanoo is armored susanoo. His susanoo is enough power that it's sword defeated nagato, and nagato is billions of times stronger than mei terumi.
3. Sasuke's intention was to find danzo. He didn't wanted to fight mei terumi. And sauke didn't used amaterasu, genjutsu, or anything to her.