A lot of the argument against the WarHound is that Marines are already more than enough AA for TvZ, and even Thors are mostly unnecessary so why are they trying to make a better Thor?
I personally have hated the Marine since beta. To keep from ranting, there is simply no reason to not make marines in SC2, even when faced with their "counter units" they are so cheap and effective that they should always be made.
As Zerg, currently, nothing in the game trumps marines. Banelings are mostly ineffective and infestors require 150 energy to kill X marines. Both units being high in gas cost and limited in their utility.
Protoss has it slightly better with the Colossus, unfortunately, that unit is just badly designed in general. HTs with storm are effective when the storm lands, unfortunately Marines move so fast, they often only take 30-40 damage before making it out, leaving them with 5hp, but their full DPS. Archons feel a lot like banelings. Nice if they hit, but generally ineffective.
TvT, I feel is actually the worst offender. Marine tank dominates the MU, and in pro games you often see silly displays of marine absurdity where one player has 10 marines and 10 siege tanks vs his opponent with 30 marines. It doesn't make sense that the 30 marines win the fight when looking at the cost of the armies, but they do... because they're marines...
So I ask: Are Marines OP? And if they are, why isn't Blizzard doing anything about it?