Playing a bit more Sentinels and looking in on the community, I find that some of the heroes and villains are extremely swingy and can go from steamroller to steamrolled based on a lucky draw, especially at higher difficulties. Cosmic Omnitron can potentially defeat the heroes during initial setup, Citizen Dawn can potentially prevent the players from ever having any cards to play (not a technical first turn loss, but a guaranteed loss from setup), and Wager Master can potentially win or lose on the first turn.
Some people like the higher difficulty and say it feels like a more satisfying win when you overcome the opponent. I look at that, and it feels more like luck that you had a chance to win at all. You can make the right decisions and improve your odds, but even at their base difficulty, villains like Cosmic Omnitron and Akash’bhuta can get a lucky draw and play 10 cards in a turn. Granted, that can effectively be an enrage timer, in that you need to defeat the villain before that roll of the dice comes up, but it still makes winning and losing more of a roll of the dice than I usually like in my strategy games.
I am using Sentinels of the Multiverse as my example here, but it is far from the only game where the challenging content has a significant luck-based factor on whether it is “challenging” or “impossible” (or, if luck goes the other way, “accidentally trivial”). That’s not a satisfying challenge for me.