OK, but Clapton is nowhere near the artist Hendrix, Page and Beck were/are.
He is an incredible technician and within his own right an artist, but he never moved beyond the Blues (Except for a few financially motivated forays into Pop) He's "great" but he doesn't belong in this discussion.
Page was a true innovator as well as being a brilliant player, however his movement as an artist beyond Rock was limited to Indian/Arabic themes.
Hendrix was a genius, but he died very young. Beck isn't the genius Hendrix was but his artistry has endured and evolved for decades beyond Jimi's death.
If you want to argue that Hendrix was greater than Beck based on his short lived genius, I'm not going to give you a hard time, but the Greatest Guitar Artist of all time, at least to me, requires longevity as well as artistic growth.