Welcome.
The key word there is 'nearly'. I do not know which parts of Hotel California were written by Glenn Frey, but as I was not there, I think it is unwise to make such an unequivocal statement. In any case, there are other parts of the music beside the guitar tracks; the melody line & the chorus line.
NB: In an interview on Page Two of this thread, Felder says he originally wrote the music in a key that was too high for Henley, so that had to be changed. To me this is about Felder's absolute refusal to give Frey credit for anything at all. This is the relevant part: Felder originally wrote the music in a key that was too high for Henley -- "When he sang it the first time in the studio, he sounded like The Bee Gees," Felder recalled. So he went back home and worked out a darker-sounding version in B-minor, a key most guitarists prefer to avoid.
Glenn Frey himself stated in HOTE that he & Don Henley continued writing the song based on Felder's opening guitar progression. I think the truth must be somewhere between the two extremes.