Jimi Hendrix was a humble guy. Hendrix was a great guitarist, but he was no 'greatest of all time,' or anything. Since his early death there have always been folks who do think he was 'greatest of all time,' but I don't think those persons know a whole lot about guitar playing. Terry Kath was fantastic, and a fantastic singer besides. I believe Jimi Hendrix also once said Rory Gallagher was better than him as well. I believe Kath was deciding he preferred the Strat over the Tele before his early passing.
My personal opinion on great guitarists like Kath, Hendrix, Gallagher, and others in the blues-rock style, or any other genre is - you get to a certain level, and who's best is only a matter of opinion. There are far too many genres of guitar playing for any person to be 'the greatest guitarist of all time.' But since we're kind of on that subject, when he was alive, many people believed Flamenco guitarist Paco de Lucia was the single most advanced guitarist in the world.