I've done a little research on Sam and Dean (by which I mean watched a handful or YouTube clips and read past Rumbles involving them - meaning I've seen what a number of Rumblers have said about them in the context of a fight).

They have a nice fighting technique, but they don't look beyond human. They appear to win due to exploiting opponents' weaknesses, by having assistance from a powerful friend, or by sheer dumb luck.

Rumbles consensus has them being beaten handily by Arrowverse Oliver Queen and low-end comic book peak humans (like Jason Todd and Roy Harper), and even losing to Bill Shatner's Captain Kirk one-on-one. It was also suggested that Michael Keaton's Batman (valued at "2") could beat them both in a handicap match.

While I absolutely accept that they've defeated some powerful foes, they've had plot armour and circumstantial assistance - just like a number of other characters in this list who are low in value - so I'm fairly happy that they should both be added with the valuation of "1".