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.
To cover this weakness of Rimuru, Altair from Re:Creators was included in the team, she has incredibly powerful Plot Manipulation, can freely see everything as fiction and manipulate entire stories and multiverses.
If - for whatever reason - you think Altair's Plot Manip - while indeed powerful, still isn't good enough to deal with Thanos when he had a story-bound One-time-only Buff - then there's also Shallow Vernal, who can simply End stories up to several layers into Outer.
Team should win this easily.
But about scaling
And only shallow vernal here reach outerversal level from what i know