Suggestion on difficulty.

I'm 100% in favor of high difficulty in games. And some fights in HoD are definitely hard. They aren't the right kind of hard though.

I find that in difficult fights I usually end up loosing from one of these ways:
My screen just doesn't register my finger swipe as quick or accurately as I'd like and I end up missing on a movement or target change, leading to a hero death.
I have to do long elaborate kiting to win a battle and it eventually breaks down because of the aforementioned problem with my phone not picking up a finger swipe.

A fight being considered difficult should be because strategy is required to beat it, not because you have to "make sure your phone screen picks up all 200 finger swipes in a row without missing any." Kiting being a requirement to defeat harder encounters is a major cause of this. The battlefields being so small is another reason that successive micro-movements are essential and a single finger "mistouch" proves deadly. Not sure if anything can be done about the size of the battlefields... we're playing on smartphones after all. But I think reducing the amount of kiting required would really go along way to making the game more strategy dependent.

So why is kiting required? Because I'm trying to win a battle against enemies that can ripe down my tank even with 2 healers in the group. 2 solutions... you can either kite the enemies around while a ranged DPS kills them, or you can get better gear. Getting better gear does reduce the need for kiting... but it also eliminates the difficulty of the battle. I don't want the game to necessarily be easier. I want to be put in a position where developing a strategy is required.

There was another way that I would lose a hard battle... my skills would be on cooldown. To defeat a difficult battle, use of skills at the right time in the right way is essential... to solve this problem, I had to result to kiting around the last enemy of each screen until all cooldowns were ready, then finish the last enemy and move on to the next sequence. While effective... it's not fun. I suggest having skills reset their cooldowns on each new battle sequence. I choose battles that are hard (aka fun), and therefore require the use of the skills for each battle. This requires me to waste a lot of time resetting my cooldowns between sequences (not fun).