Mythstones should increase as enemies do

Title really says it all. It’s a bit odd that beating a boss at lvl 75 gives you the same mythstones (1) as beating a boss at lvl 25. They really should scale up at least a bit. I know the rewards for prestiging go up as you get farther, not ignoring that, it just doesn’t make sense that beating an epic boss at any level only gives 1 mythstone.