Balance will always be imperfect. Heros are changed to be stronger/weaker every patch. I would imagine its the same for Dota?
At any given time, you will always have X heros for every roll that are way better than the rest.
New heros aren't always overpowered. Most of the heros that are changed with every new patch are pretty old.
I mean sure as a player I find it frustrating that I have to bank up on IP, but I understand Riot's view as well.
Honestly if all you can buy in Dota is cosmetics, then I really don't understand how they are making money. (but then TF2 pops in to mind, so I guess there really are enough people that care about that stuff)
I think your term "soft pay to win" nails it. I don't like just "pay to win".