So now we discussed about sasaki vs Denjiro..
I think Oda has shown to us how to compare the power scaling between these two..
1. Denjiro/Kyoshiro power level.
Oda has shown to us that several red scabbard member has the power equal to Jack, the all star. Those are Nekomamushi, Inuarashi and Ashura Doji. I wouldn't be surprise if Denjiro also able to do the same feat like Ashura Doji, as him and Ashura Doji are the only one who survive when they fight againts Kaido and his army. That's definitely not an easy feat.
2. Sasaki power level.
Even if we haven't been given any information about this guy's power and abilities from Oda, but based on his position as the Tobi Roppo, it has already say something for this comparison. All star, in general, has a higher power level and position to that Tobi Roppo. That's all we know. No assumption here. As for Sasaki and who's who challenge all Star member, it still doesn't justify they are already stronger than all star. They just challenge them. But that's it.
So, with Denjiro most likely on the same tier with other red scabbard member (Ashura doji), and Ashura doji is proven to be equal against Jack, the conclusion if Denjiro and Sasaki fight most likely will be:
Denjiro > Sasaki (with high difficulty, at most).