Blizzard does not care about making a solid competitive experience, at least not first and foremost. Their goal is to make a game that caters to the largest demographic (Casual and mobile players these days) and make it easily accessible to be successful as possible.
Look at WoW, PvP has fallen very far from its former Esport glory thanks to their design philosophy. People have wanted separate PvP balance from PvE for years as it would make things easier to keep in check. But because it wouldn't be in the casual players best interest (makes game more complex) they haven't done it. And as a result, in trying to keep things balanced, they completely homogenized each classes toolkit to keep things as fair as possible at the expense of class diversity and game feel.
Hearthstone is relatively new, but unless something changes they will break the meta to the point where competitive is completely unplayable unless they implement formats or ban lists. Its simply impossible to keep the game fair and balanced between classes as they add more cards, eventually something broken is going to come through and they have a horrible track record of nerfing powerful cards that dominate the meta. Look at games like MTG, Pokemon, or even Yu-gi-oh. Its not like they have an extremely diverse meta to begin with, every deck is a variation of beatdown as they haven't made a single alternative win condition. Most popular decks over the past year have been focused around building OTKs that are hard to counter because of their effectiveness and it just isn't interesting to watch or play in my opinion.
That isn't to say the game isn't fun or well made. You just have to realize at its core its designed as an extremely casual game with many mechanics relying on luck and not at all focused on a serious competitive scene. The focus is on ease of access and fun, and one day those design goals are going to hurt the top end hardcore players.
Overwatch will be a good game, they haven't fired their good developers and they have a ton of money and time to throw at it as well as a devoted following. But they really don't care about making a balanced and compelling competitive experience. It will be there for awhile, people are driven to throw themselves into blizzard games like that. But be warned, they will not listen to the requests of pro players if it isn't in the interest of the lowest common denominator. Look at hearthstone, entirely disregarding the beta phase, its taken them over a year to even consider adding new deck slots despite overwhelming support from the community. They site back-end statistics that most players have 1-4 decks, even though its the vocal minority, the 5-10% at the top who buy the packs, enter the tournaments, and do everything they can to support the game are the ones who will actually make use of it.
Overwatch, Hearthstone, and Heroes of the Storm come from an entirely different design philosophy than previous blizzard titles like Diablo 2 or Warcraft III (Still my favorite RTS of all time). They are expansions by the company into new game genres to reach the widest audience possible. They are being made to be easily accessible (Free to play, simple mechanics) and highly monetize-able (Premium features/cosmetics). Blizzard isn't stupid, it makes perfect business sense. But people have to realize there isn't much money to be made for them by making a compelling competitive experience, so it will always be an afterthought. I don't get how people can quote CSGO devs and expect Overwatch to be any different. There are still pretty bad bugs that existed in the hearthstone beta that have yet to be fixed. (Nozdormu breaking timers, Cards shifting on placement, etc)