Personally I think Duelyst might encounter a problem with power creep in the future IF the new expansion cards (and maybe some core cards, actually) are not handled properly in a balance patch.
Textbook example: Enfeeble. Consider: This card comes dangerously close to a full board wipe on three mana. Because of how irrelevant 1/1s are in the grand scheme of things, an Enfeeble even without Blistering Skorn is still massively impactful. The whole “it’s balanced because it’s symmetrical” is really almost irrelevant for a lot of reasons, but a very simple one being that Enfeeble still stands very high above the power-curve for a three mana card despite the downside. I’m not sure that there’s even a single three mana card in Duelyst that represents the amount of potential power Enfeeble does. (I personally think Enfeeble should be four mana, which is more in-line with full board AoEs such as Decimate and Pandamonium).
Now that Enfeeble is a thing however, any future three mana cards have to be compared to it. Is new card X as powerful as Enfeeble? If yes, include. If no, exclude. The devs will have to start printing cards that compete with Enfeeble’s effectiveness at three mana, and eventually all the formerly OK three mana cards will be thrown into the trash bin. Obviously this is a simplification of the issue but that’s the basic premise. See this video on a more detailed explanation of how power-creep works / starts.
I think there is a similar issue with things like Concealing Shroud, Trinity Oath, Punish, etc. But of course this is all only hypothetical, and I hope the next balance patch will shake the meta up considerably. Overall, I like the expansion for the new cards and mechanics that it’s added in, but I hope the imbalance doesn’t go unnoticed.