Maybe not quite the same, but I have had to remove old Cetol before, and it leaves a very hard "plastic like" surface. (At least the parts that had not weathered away...)
I went with 80 grit on a Makita palm sander. To protect the adjacent cabin surface I would slide a piece of thin sheet metal along the base of the teak rail to keep from scratching the non skid. It was still time consuming work. If doing it again, I will park my ol' shop vac on deck and put the intake end of the hose beside the sander. I learned to do this when sanding and grinding some glass inside the cabin. It cut down 95% of the mess.
I touched up the teak rails with some 120 grit, and then laid on several coats of new Cetol. Then (the most important step!) we put snap-on sunbrella covers over both handrails whenever we are off the boat. It has been 4+ years and the rails still look great.
I know little about varnish removal, per se, because I do not use it on exterior teak. We do use lots of varnish on the inside. On the few places I have had to remove the interior varnish, I also started with 80 grit.
As yet another "plan B", have you considered a heat gun to soften the varnish? I see the pros using these on boat exterior projects quite often.
Best,
Loren
Olson 34 #8, Portland, OR