"why X skin provides Y bonuses?! I love skin but why can't you make great bonuses for that? why you did great bonuses for another skin I hate it so much"
It's been proven by so many top games already that cosmetics shouldn be involved into hero progress system.
I honestly have stong feeling it's just because of players' low expectations, like "hey devs how about adding value to existing thing? it's sure easier to do that something new".
If we ever have skins with bonuses we will have cries about unfair treatment (if skin would be rare), cries about why this skin is so ugly but gives such good bonuses, cries about why this awesome skin have such crap bonuses, you name it.
There's like a 100 and 1 things you can make and add to hero progression, we already have:
- skill levels
- gear stars
- rune sets
- rune stars
- rune enchantments