How can we measure a character's power level in relation to others for the Dragonball Series beyond Frieza?
After the concept of power levels was dropped, power scaling was done throughout the series by referencing one character to another. This was essentially done by the characters themselves sometimes. In terms of Dragon Ball Super for instance, In the ROF Arc, Frieza tells Goku that based on the power he senses, he should be stronger than Goku which kind of Establishes Golden Frieza is > Super Saiyan Blue Goku. At the start of the fight, Goku tells Frieza that he's gotten stronger but he doesn't need Super Saiyan to fight Final Form Frieza. So at that point in time, Base Goku was > Final Form Frieza. In the tournament of power, for instance, Goku and Vegeta more or less say they have never experienced a level of power as strong with reference to Jiren indicating Jiren is stronger than say, Fused Zamasu or anyone else they fought before that point.The problem with your scaling technique is how exactly would you quantify the difference in power with numbers. For instance, Toriyama at one point said Goku was a 6, Beerus was a 10 and Whis was a 15. This was at the start of the B.O.G arc. Goku Grow substantially stronger however, disregarding Ultra Instinct, he is still completely shadowed by Beerus's level of power. We know this based on the fight between Mastered SSJB Vegeta and Beerus in the manga where the latter one shot's Vegeta without even fighting seriously.The second main problem is characters grow several times stronger(Especially the Saiyans), during the course of the fight. For example, Goku who fights Jiren in Episode 109 is substantially weaker than the Goku who fights Jiren in Episode 122. However, both versions of Goku's were indicated to be vastly superior to Jiren who wasn't even trying. So displaying this difference numerically, wouldn't really make sense.As of now, I believe the characters are scaled by the writers themselves during dialogue between the fighters themselves or in the form of side commentary from another fighter witnessing the fight.