There is no easy solution with such thick build ups, especially given your experience with #36 grit paper.
I know of no easy solution.
3 or 4 passes with DADS Easy OFF Paint remover would work however, it is about 1/4 as toxic as the most popular paint removers on the market and easily twice as fast.
I have used a lot of it, be sure the room is well ventilated and that you use a rated respirator and heavy rubber gloves.
It can be a bit hard to find, many lumber yards carry it however.
Given the gummy nature of the old finish any sort of power plane or rotating head cutter is going to clog up too fast, or cut deeply into the floor, posing a whole new set of problems.
I think in the end you will be stuck with using a stripper, then the standard floor sanding protocols and equipment.
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