I upgraded from the 12 Pro Max to the 13 Pro Max. At first, it was underwhelming. After using it for about a week, the 12 Pro Max is noticeably less fluid. The ProMotion display is very granular/subtle at first, but then quickly becomes a top feature and easily detectable between the previous generations. The interface transitions feel “swoopy” to me, almost like I’m dipping a ladle into a bowl of punch, and the rendering does not soften as the interface elements and on-screen text/graphics move around. Hard to describe, but that gets close!
The camera is also less sluggish and klutzy, especially when transitioning between photo modes.
I agree with OP, and I recommend the upgrade from the 12 Pro Max, especially if you can avoid a big depreciation hit. Apple is offering $785 trade-in value.