Israel genealogists who really take this stuff serious don’t dispute it unless neo Nazis hijack the data
No question the King of Khazaria converted to Judaism and much of his territory did too
Where Sephardic oriental and Ashkenazim all evolved from is speculative though I have no doubt given their fixation on maternal identity that they sure have some ties to Judah
What percentage who knows
That could be. I did read a shorter version of Koestler on the Khazar theory and it sounded plausible. I just didn’t want to spend time following the resulting debate over whether or not it’s true. Koestler himself was Jewish and wasn’t advancing the theory to cause any harm.
The Khazars wouldn’t have been unique in converting to Judaism. The Idumeans, which included the Herod family, were converts to Judaism. That didn’t always sit well with the Jews who weren’t converts.