Yea, that's the one saving grace. But even then, each roster spot you open up costs more 'purple currency' at an increasing rate. Not to mention that you will need to keep leveling up all those 'extra' heroes.
Which means even more grinding.
I think the game will be fine as long as I just play it an hour a day. Trying to play more than that will probably cause me to burn out on it. I'll just completely ignore the multiplayer aspect to it.
I'm fine with paying $10 or $15 for a high-quality experience, so would that be enough money to enjoy this game?