Could Blizzard have “all data?” No. There will always be statistics that no one even thought to collect.
How much statistics gathering does Blizzard actually do themselves? Well,
If Blizzard chooses not to create an algorithm to recognize the major metagame archetypes, track winrates at various ranks, and several other statistics, Blizzard knows that websites like HSReplay and Vicious Syndicate will literally do all of that work for Blizzard, providing all of the same results without Blizzard lifting a finger, and in the case of Vicious Syndicate for free and at a very high level of quality. All Blizzard would have to do is release new cards then wait about a week.
So Blizzard has a strong incentive to never develop algorithms that scan deck lists to determine their archetype, never track deck archetype winrates internally, and never construct archetype matchup winrate tables internally. Thus, we can assume that Blizzard has access to the same data that we do, from the same sources.
This would fit well within Blizzard’s overall modus operandi. For example, in Diablo Immortal, developers made no serious effort to balance drop rates between various farming dungeons, at least not on their own. Instead, they hosted a closed beta test for Diablo Immortal, and a team of unpaid volunteers took the task upon themselves, using the best speed clearing strats to do multiple recorded runs of every dungeon, watching the recordings to collect drop rate data, and entering that data into spreadsheets for analysis and comparison. This team then submitted their work to Blizzard, completely unpaid, who acknowledged their work as the basis for drop rate rebalancing.
In short, Blizzard doesn’t pay for balance testing for Diablo Immortal, because unpaid beta testers will do the work for free. So would it not then follow that Blizzard wouldn’t pay for balance testing, to include data collection, for Hearthstone, considering that we know that players do this work for free as well, via the Hearthstone Deck Tracker’s data collection to a third party website?
In all seriousness, I don’t know exactly how much data collection Blizzard does. My real point here is that demonization is NEVER a good predictor of behavior. Why? Because there is only one way to to be perfect, but there are infinite ways to be wrong — many of which are mutually exclusive to each other. Is Blizzard wrong by collecting data then using that data to nefarious ends, OR are they wrong by being too lazy to collect the data in the first place? You can’t tell this with a demonization model, so instead what a demonization model becomes is a manifestation of pure raw confirmation bias, seeing not what is but what YOU want to see.
Stop strawmanning opponents of your demonization model as “defending Blizzard.” I’ve already shown how it’s possible for someone to have a negative view of Blizzard that conflicts directly with your negative view — that is, that Blizzard is very lazy. There are infinite ways to disagree with your demonization model and only one of these infinite ways is the belief that Blizzard is perfect.