Rory Gallagher was a great, yet underrated guitar player who did not get anywhere near the amount of credit that he deserved. He was not as famous as Jemi Hendrix, and he may not have revolutionized guitar playing the way that Jimi Hendrix did, but he still was an incredibly skilled player.
Jimi Hendrix had performance ability. He was a person that people liked to go see. The people bought the tickets to see him. That doesn't make him the best performer. Rory Gallagher what a much better technical player. He could play more difficult things and his tones were more pure and harmonic.
Hendrix in comparison was much more of an innovator, explorer and pioneer of new musical directions. He also had copied the same black American blues men, but he wanted to take that music somewhere new. Hendrix was similarly untrained in musical theory, but he was clearly a more accomplished all-round musician being a more versatile and inventive lead guitarist AND rythym guitarist.
But the reason why he is regarded so highly by his contemporaries was not only that he also could play with great inventiveness, sensitivity, lyricism and with much 'feeling', but that he furthered greatly the sonic scope and possibility of the electric guitar in popular music with his bold and unapologetic use of feedback, white noise, loud amplification and special effects.
I think Jimi Hendrix paid Rory Gallagher the best of compliments by saying he was a superior artist, and maybe in certain respects he was, but Jimi Hendrix is possibly the best American guitarist. There are many great guitarists but few set themselves apart like Jimi Hendrix. He is truly a legend.