Guys,

is it true that the force of a depowerable kite is equal to a non-depowerable kite 2 sizes smaller?

say a the force of a 7m depowerable = 5m non-depowerable?

7 m depowerable would be about 5 to 3 m foil comparable wind range. So yeah, kinda true!

Yup.
I have a direct example I have an Ozone Access 6m and my friend has a Rage 4.7 He rides a flexi wide wheels and I was using a PL wide wheels, we are close to the same weight we buggy together and stay together and things like soft sand and bearing issues one would be a bit faster. The place where it made the biggest difference is when he would be on the edge of overpowered then I can pass him at will and in the real light wind we could walk away from me (I am a bit heavier and his kite works better in lighter winds all fixed foils do) We both think the kites are quite an even match.