The 70's has the most good songs by far.
Early 70s had some great songs and Elton John and Billy Joel emerged. Then came Disco and ruined the decade
Elton John and Billy Joel
An interesting phenomena...
If you listen to both of them you will realize how many melodies BJ ripped off from EJ.
I bet when they went on the Piano Men Tour, it was because EJ was threatening to sue BJ.
No, I don't hear that AT ALL. Never occurred to me, not once.
Elton John did mention Leon Russell as a strong influence, speaking of yet another artist not mentioned in the OP's list above, but I don't hear a musical similarity there either. Why don't you post us some comparative examples.
As for which "came first", I have a Billy Joel album (his first) that dates to 1971 for what it's worth.