My feeling is that G1 straight-line segment approximations will be fine but you need to start with a smooth curve model, not faceted as per STL, so the CAM process can sort out better approximations. Not sure why you seem a bit "anti" G1? I know it feels counter-intuitive but having done a fair bit now with F360 I find it often produces lots of g1s where you would expect curves, but the only downside seems to be file size. I've ended up with gcode files for quite small parts which have maybe 75K lines of code which are generated by the adaptive cutting strategies, but after my initial surprise, I now just shrug! In the days when machines read files from floppy disk, that would have been pushing the storage limits but these days, even a smallish memory stick holds 10000 times that so it just ain't a problem. As long as your motion control software/hardware can then do the constant-velocity stuff to smooth out the corners and with decent MC hardware this isn't rocket science.

Or just build your spreadsheet to generate one G2 per vertical step, and calculate away! I'm sure that that will work. But my IT background says that if a machine can do the work for me, then I'm not going to spend brain cycles doing it by hand...

Good luck either way.