I've got one which I guarantee you will immediately ask me how the Hell it is a "brain" game but really it is.
Marvel: Midnight Suns. Done by the X-Com team and if not an outright disaster, certainly performed far, far below their hopes. It's wrapped up in exploration and social story aspects with a lot of both of these things, but the very heart of the game is a puzzler. At every stage when a new difficulty unlocked, I put it up. Until by the end I had reached Ultimate III which is as hard as it gets. And this game was one of the most challenging games I've ever played. It doesn't look it.
Battles are, barring the initial power shuffling, deterministic. So you can replay a challenging battle over and over with a dozen different forking decisions trying to work out a way to beat it. For the final battle I had pages of notes, trying alternate strategies, branching off at the tiniest little differences - attack that enemy not this enemy, play this attack first, then that one, use the damage boosting item on Hunter, not Ghost Rider, ad infinitem. At multiple points in this game I thought I had come to a point it was simply not possible to beat it, walked away, came back the next day, saw a strategy I hadn't tried or changed my roster and gave it another go.
If you like Marvel (and it leans more to the comics than the MCU) you'll probably enjoy it. If you enjoy RPGs and exploration games that's a plus. But... you don't have to complete everything and can focus more on the battles and mainline story. There'll still be a whole bunch of stuff aside from the battles, story elements, friendships developing with the other heroes (and that unlocks additional power effects you can use in battles). Apparently one of the reasons it did badly was that people thought it was a "card" game. Whilst that is the visual way they represent it, really it's a game of carefully selecting and developing useful powers and understanding how to synergise them and defeat a series of ever more difficult encounters. After a certain amount of encounters / story progression, you get to unlock each new difficulty layer. There are also these set puzzles that you need to do in order to unlock the ultimate cards and some of those puzzles are very hard.
I can't say it's exactly what you're looking for because I've no idea if you'd like the exploration and social / storytelling aspects of it. But despite all appearances, the actual combat is exactly what you're looking for. Hard as fuck and a tonne of hidden complexity.
I thought of the battles as like extremely complex sudoku puzzles - there is always some combination that will work. You just have to find it.
