Are Simon and Garfunkel considered rock legends? I mean is their music considered rock?
Yes, they are legends and yes, folk rock is the music they're known for.
“Rock” has been a very loose term to describe popular “music” for decades.
Among the last genuine rock-and-roll acts were The Sex Pistols. They eschewed their induction into the “Rock and Roll” Hall of Fame. They wanted nothing to do with it and wrote a nasty letter saying so. That’s the spirit of rebellion that used to characterize rock-and-roll. And it dies a bit more whenever someone is gleefully inducted into it.
Recognition is awesome. Awards are cool. But it’s best when it comes from fans and not some self-appointed “Hall of Fame” body. The R&RHOF is (IMO) the antithesis of rock-and-roll.
Rock is not just a macro-genre that covers many styles. (Country Rock is Rock, not Country.) It is also a technical term for a certain kind of beat and rhythm. In other words, the word is ambiguous.
Many Gospel choral pieces say “rock” on the score; it does not mean the genre, but the manner of playing. The music is not “rock music,” but it is done in a rock style.
If one goes to AcclaimedMusic.net, one will see a statistical analysis and aggregation from all major critical lists - worldwide - of popular albums and songs going back decades. (The statistician who wrote the program is Swedish.)
For years, the consistent results from the algorithm have proclaimed the consensus for best popular album of all time to be:
“Pet Sounds” - by The Beach Boys.
Today, many would regard this as adult contemporary or some other sub-style of rock/pop, but it has always been classified as rock music. It is now sometimes called the precursor to the sub-genre/sub-style of Baroque Rock/Pop or Avant Rock/Pop.
(Both Paul McCartney and George Martin have said it was the inspiration for Sgt. Pepper’s; they certainly regarded it as rock music.)