Well the in game message says higher lvl bosses have better drop rates. I have not once seen a good reward come out of higher lvl relic hunt. I get the same at lvl 40 than I do from a lvl 20.
That really doesn't matter. The best you can come up with is a 2 star in a silver chest and 3 star in a gold. It's the same in 20 as it is in 50. You would think that a relic hunt 50 would at least give you a 4 star to help out with raising mastery level.
Lvl 40 and 50 raids do give 4☆ items now. I've confirmed it myself by pulling em. Ofc the gold chests are the only ones that will drop them which is how the system should work lol.
Welcome to the world of rng. No matter how the ratio is, there's always the chance of going against the odds or vice versa lol. My pulls have been pretty steady at 50s with 4☆ so no idea.