Bobby Fischer himself denied being a Jew, wrote to Encyclopaedia Judaica to have his entry removed, denied the Holocaust, expressed anti-semitism, and said in an interview he was not circumcised.
https://stljewishlight.org/arts-entertainment/jewish-or-not-bobby-fisher/
Bobby Fischer was stellar in 1971, defeated Spassky in 1972, but that was it.
Kasparov is regarded as better
http://www.chessmetrics.com/cm/CM2/PeakList.asp
Period.