IMHO there were only 2 giants of 20th century: Segovia, and Bream. Add Paco de Lucia for modern flamenco, and that's it. And there are/were 10-12 other great guitar musicians after WW1 as well who for various reasons fell short of becoming giant.
And you can burn me at the stake if you wish, but John Williams is not in this list IMO. Virtuoso - yes, financially succcessful - yes, influential - yes. But he did a lot of harm to classical guifar IMO, and I do not mean promotion of Smallman here. Thanks to him we now have dozens of popular 'virtuosos' who sound completely blank, and this is not direction I'd like to see for CG. I've read somewhere that having perfect pitch does not mean being good musician. This is exactly about Williams. His obsession with perfect techniques, perfect rhythm makes his play impotent IMHO. Things might turn different if he did not join the band during his early years, but it is what it is
I hope I have not opened the Pandora box here