Boat’s are a compromise and the shackle and swivel connecting the anchor chain to anchor is usually the weak link. Check out “Red Pin” shackles at Hamilton Marine. These are USA made and meet Fed specs. They will still be the weak link but at least you can trust the quality and working load rating.
I looked at the spreadsheets but without knowing how the author derived the results it difficult to say if they are right or wrong. We have tendency to trust computer generated data without questioning how those results were derived.
Why not use 125 ft of 5/16 hi-test chain connected to 1/2" Dacron polyester double braid or 5/8" 3-stand nylon?
There is not perfect anchoring system.
Rod