Looks like you've checked everything pretty thoroughly. 0.001 is very good for miter-slot to blade alignment and I doubt you'll hear anyone telling you to dial it in further. Also the runout of 0.0015 on the blade is quite good, translating to an arbor runout of much less than 0.001.
To be honest I am not sure what is causing this, in particular the curve to the cut. The only thing that still stands out is the fence...if it's wonky then it can be putting side forces on the blade as you feed the piece through which might contribute to the weirdness you are seeing. However you say it does the same thing if you use the miter gauge, so the fence can't be the main problem.
The only thing I can think of is that the piece is somehow rocking as you feed it through. It starts out angled a bit away from the blade, so you get a deeper cut on the bottom, then it angles in towards the blade (or vice versa). This could be due to the table not being flat or the workpiece not being flat. It could be quite subtle and cause the issue you are seeing. Maybe focus on flatness just in the area between the miter slots, checking for twist as well. See if a flat piece rocks even slightly as you press down in different areas.