I know certain turn things got broken after some mill stuff got fixed in the .066 version, however I can't remember what they were. Turn has always been the poor relation with Mach3, as it's got very few users compared with Mills/Routers.

What manual are you reading?
I've got the one named Mach3Turn_1.84, and the only things that have changed are the number of pulleys allowed has increased from the 4 mentioned in the manual to 15, and the pulley configuration is no longer under the spindle set-up tab, but has it's own option in the Settings menu. Other than that, it still works the same.

Essentially, configure your spindle motor output so the motor runs at maximum speed, then set min/max speeds and ratios for all the pulleys you want to use. Then Mach will display an error if your commanded speed exceeds the currently selected pulley.
Remember it will be upto you to manually select the pulley in Mach that matches what one you have engaged on the lathe!
Also, even though Mach can display an actual spindle speed (STrue), it does nothing to close the loop. It only needs the actual speed to sync the z-axis for threading moves.
I actually just had a quick search of the mach support forum, and the spindle calibration does work, but it's advised not to play with it! - spindle calibration

G70-73 are only fundamental if you're used to using them. The turn wizards will create the required g-code for the non-profile moves.
You've got to consider how much Mach3 costs in comparison to the controllers you've mentioned.