Sanding vs Stripping?

I’m working on removing a very heavy buildup of solid stain from a redwood deck. Somewhere in its 40-yr life the owner switched from oil semi-transparent to solid. After scraping the peeling areas I’m trying to sand off the remaining solid, expecting to also need to strip due to crevices. I started with 40 grit and rental orbital sander and it is barely making progress (I had hoped to spend 1 hr per 100 sq ft sanding, I have about 700 sq ft to do.) 3 hours on that 10x10 patch still barely made progress. I then tried stripper, which made some progress on the remaining buildup but appears it would need a few additional treatments. Any suggestions of how to speed up this process? Photo is representative of peeling areas, about 1/3 of total surface is peeling and most any board can be worked on and the stain lifts in patches.  The boards are 2x6 and mostly sound so it seems worth refinishing and hoping to go with semi-transparent to enjoy the redwood. However could resort to solid.