Michael, in your experience how much difference would it make that at least some of these people are not using modern nylon strings? I don't know enough to even speculate!
They are using Gut or Nylgut - a synthetic equivalent. Oddly enough some Nail players also use Nylgut. It does make a difference but hardly night and day. The flesh players tend to use lower tension strings and strings that are less highly polished. That helps with the pad of the finger 'gripping' the string. Don't forget that the majority of players in the early part of the 19 th century did not use nails, that includes Sor - one of the giants of Guitar composition. Francisco Tarrega switched to playing without Nails late in his career, supposedly because he suffered some medical complaint that affected his nails.
There are good no nail players who use a modern classical Guitar strung with Nylon. Not many but they do exist. There's a good example on U tube but I can't find her! she's on there somewhere.
Although it's not 'modern technique' you certainly can play Classical Guitar without nails and to a very high level. It does take time and application to develop the technique. Switching from Nails to playing with flesh and you are highly unlikely to master it in just a few months.