Your combat scenario exists in any game where a characters has 100 abilities and 5 hotbars. What you basically want is to give players a myriad of skills to use because some creatures might be resistant to some and not others.
Here's the problem, once someone does this dungeons once then everyone on the internet knows the resistances. Even if you never look at a website or a forum, you'll learn the first time and the second, you just don't cast fire spells anymore in the Dungeon of Fire Elementals. I really don't see any special type of combat here, the scenario can describe any dungeon experience I've gone through in almost any MMORPG in the last decade. Especially in a new game where you really don't know what to expect.
Rift did difficult dungeons in the beginning but then they were nerfed. I'd be happy to go with that level of difficulty again.
As for Free to Play, you really really under appreciate how much people spend on cosmetic shit or extra bag space or whatever. Games make a killing with that kind of thing. Just look at dopey things like Candy Crush.
Yeah I don't really need anything wildly new. I would ideally take a MTG rip off any day, but I think that might be too much to ask, especially of an indie game. The resistances thing was just one example. There are infinite other scenarios, like if your group gets jumped and things are going bad, do you focus on nuking one mob dead, or do you help out with healing, or do you focus on crowd controlling some stuff. It's different solutions and each could work well or badly depending on the situation.
And yeah it already happens in games but the difference is that in modern games - none of this shit ever matters. Take Rift for example, there is basically no "cast time" on spells so you don't have to choose one approach to a problem. In the above scenario you can just do all three... heal a bunch of people in 1 second, then sheep a mob or whatever in another second, and then nuke the hell out of everything happily. Vanguard is the same more or less. Also mobs die so fast, there is never really any need to crowd control or focus on some long term heals over time or anything. Because the best option is *always* just... 1,2,3,4,5 spam the hell out of everything with your lightning bolts and everything will be dead in 5 seconds. So that's what I want to see done properly, every mob to basically be like a raid boss, ever mob takes at least a minute to kill, so that when you get 5 of them in a dungeon, it's a big fucking deal that people think OH SHIT! and you can't just spam your routine and watch everything drop dead. Someone needs to crowd control, maybe more than one person, the healer needs to save multiple people multiple times, the tank needs to run around desperately trying to aggro stuff and smack stuff, and the dps need to be careful about which targets they pick because nothing dies fast, so if they all shoot different mobs the group will die. You have to focus fire on one mob and get it down, and you better be sure to use the right spells too. Sometimes its better to cast a slow/debuff on a very fast melee mob than it is to just nuke it.
And the thing about resistances doesn't matter. Everyone will eventually know everything anyway, spoilers or not, but the point is that people need to actually learn from their experience and then apply that experience. That's what separated good players from bad in EQ. A good player would see that maybe a mob had a damage shield so would disengage it and hit something else until it got dispelled. Or if a mob has a resist they would stop trying to nuke it with a spell that might not work very well and use some other spell instead. It doesn't matter if there are spoilers online, what matters is that if there are random scenarios that regularly happen in group play that you need to react to, a good player will make the right decision, and a bad player will potentially screw up so bad that it wipes the group. That's what I want. There were resistant mobs in EQ too but there were 100 other things that players needed to learn how to handle and if they didn't handle it, bad things happened.