To me more skill variance is already enough of an edge for premium heroes and increased stats shouldn’t widen it more.
Luckily we are still not to the point of throwing old heroes into the trash bin and hopely V20 would address most of the balance issues…
Follow the link to know what I think about comparing core heroes with Premium ones.
Of course we could compare them with core heroes specials as they are still part of this game (and some part of them are even better than the premium heroes, see Brienne vs Khiona) but in their overall skillset it’s clear that premium heroes greatly overwhelm the core ones.
Expecially since there is almost no competition into the same tier when it comes to status effects, where 4* and 3* heroes have more skills variance.
This is no naivety: we don’t want for core heroes to be premium heroes’ clones but gradual empowerments of newer heroes is pretty much what would bring powercreep and too much of it would be bad.