Art costs (measured in man-hours) are one of the more predictable aspects of game development, they scale well and can be outsourced easily.
I certainly have my criticism for the game such as the slow card releases, RNGfiesta, and lack of QOL updates, but ultimately the game is really well put together.
Though Hearthstone does have its own set of issues like you mentioned, I'm very glad they drew the lines on complexity where they did (notably no user interaction on opponent's turn except for secrets)
An exact sequence of events can be replicated with the timing of them altered and you'd get different outcomes.
Whole board affecting secondary effects can also have unpredictable interactions with cards in play's triggered abilities.
In MTG parlance, the "stack" is broken in Hearthstone.
Unless you are talking about something else and I misunderstand you? Maybe something like the order of deathrattles (they are triggered in order of the cards played, just like the few instances of time-stamp-matters interactions in MTG). Or do you mean how the max minion limit works where "dead" minions are still there during "on damage" effects but not during deathrattles? There is a few nonobvious rules like that, but I'm pretty sure the rules are actually pretty solid and not bugged.
I mean, everyone at Blizzard knows what an "Orc Warrior" should look like. Green skin, muscles, some type of weapon. But someone had to actually create new drawings of it for the game.
This means that the main challenge behind coming up with a new franchise is to come up with a consistent, compelling concept for its various elements.
Is the problem that there are lots of mediocre artists but not many who can actually execute projects? Or that it is hard to parallelize things like this? Or that once you parallelize too much, the amount of value added by a marginal artist is not enough to pay them?
I think part of it is that standards keep increasing. Compare this demon concept art from Warcraft 2 (1995): http://vignette2.wikia.nocookie.net/wowwiki/images/c/cb/Daem... to this one from WoW: Legion (2016): https://s-media-cache-ak0.pinimg.com/736x/56/f2/7f/56f27f98a...
There are probably a lot of artists that can execute at the 1995 level who aren't employable in 2016.
I would imagine artists need to be involved in technical discussion and would need to learn & bug-test custom software for importing and processing assets. It seems like a different skillset to traditional art & design backgrounds.
Looking at really prolific game studios, they tend to be in less art-intensive genres. 8/16-bit RPGs, pixel-art platformers, etc.
And the people that really crank out games on a limited staff and art budget tend to reuse the same engines and assets with minor iterations. Think Spiderweb Software[1], or SSI with the Five Star games[2].
[1] http://www.spiderwebsoftware.com/
[2] https://en.wikipedia.org/wiki/Panzer_General