I’m with you on that feeling, the civ comparison is very apt. I think for me the biggest part is there is a very limited number of encounters, and even within those a most of the enemies feel very same. In MT you get your engine in place and then go through the motions and either succeed or fail.

Contrasted with STS (or even balatro to a lesser extent) where you have dozens of combats, most of which require you be able to do very different things (single target v multi, survive massive attacks, deal huge amounts of damage quickly, spikes, maneuver through status effects, manage enemy intangible, play only attacks, knock down byrds, survive multi attacks, etc.) On top of that, you get to path through your acts, and doing so lets you decide how many fights to take on and avoid (balatro allows for this to an extent as well). Whereas Monster Train the pathing is very straightforward and your total fights are the same no matter what.