Why are you not a unity fan? I am not gamer programmer by trade but I am using unity help teach some of my younger brother to code and am really enjoying it. What do you see as the downsides of unity?
The problem is probably that, because it's so easy to get into [0], it's easy for amateurs to produce something that is at least runnable. But lacking experience or fundamentals in performance or design, it's not often something that is good.
[0] Well, if you have the patience for video tutorials and GUI interfaces. I grew up in a different age for programming training.
How can you say that the problem with Unity is that it's too accessible? That's like saying that the problem with today's internet is that too many people have access to it (and, as a result, some parts are shitty).
Signal to noise ratio may be causing a bias. There are some great things out there that most people wouldn't realize are unity. I think this bias might be caused by the free/communoty version and its overly apparent logos and default look. All the great work is probably paying for full license and thus that and other things minimize the "i am unity" stuff.
While hearthstone may be fun, I don't think it's existence speaks to the value (good or bad) of the game engine it was developed in.
It's technical excellence (esp. w.r.t. rendering) was low relative to the competition the last time I checked (~ 1 year ago). If Hearthstone is great, I suspect it's because the game designers (the people who make something fun) are good at their jobs.
Really, I suppose it comes down to the strengths of your team and your goals (fun, mind-blowing visuals, dev time, etc.). I'm sure there is a place for quite a lot of game engines to exist given the trade-offs involved.
Performance is atrocious compared to other engines.