Like, I got through this one, but I don't really know what the intended strategy is.
I wouldn't say that there are "intended strategies." There are sets of 10 cards and sometimes special stuff.
The multi-opponent levels are painful - all that waiting, endless attacking. Nothing was originally picked out with multiple opponents in mind. Multiple opponents with Council Rooms is a bummer; things will go well for somebody, and the computer knows how to buy a Council Room and some Provinces.
Edit: Not saying this one is too hard (it did take me like a dozen tries though) but, man, some of these Adventure mode levels are way harder than the rest.
Well you are testing them, is how I see it; they weren't all tested before. I played through the main set ones, although they just set me to the end on the expansions, so I could jump to whatever level, so as a result I haven't played through them.
It's possible some levels are too hard. Mostly the hard ones have only taken a few tries for me. For the main set, the one I remember is Witch vs. Adventurer, but that still only took a few tries (and only has one opponent, phew). The ones where you get a free Throne each turn, it's such a huge advantage. And then there are levels that might be hard but there's something you can do that the bots don't know how to fight; especially, levels with alternate VP. There is a reddit question about a level now and well go for Gardens dude, it will be easy.
But really, any level you think is too hard, make a list, possibly we will make some of them easier. The goal is good times.