Whew! What a question samurinja!
When our Design team starts looking at creating new Heroes, or when we're looking to do a Hero update, we definitely try to make sure that a good variety of strategies, playstyles, and counters are present in the game for players to choose from.
We do have spreadsheets that detail what each Hero is designed to be good at, what they're designed to be bad at, and what they're designed to counter. A recent example was us identifying that we lacked Warriors pointed at countering mage Heroes, but had a plethora that could counter Basic Attackers. We felt Stitches base kit was pointed toward being strong against mages, so we tweaked his Talents such that he was even more pointed toward it. Anub'arak is another Warrior that is going in this direction in a future patch.
In general, we get excited about thinking about draft implications when designing or updating Heroes (I'm sure the Hero Designers down the hall would love for me to clarify that it isn't the only thing that we look at when making kits though). It's important as our roster grows that we don't just make "better Vallas" and "better Muradins", but instead create a more diverse and complex roster to promote new and unique synergies and counters, so we don't have a revolving door of "who's on top this patch" in your Heroes games.