As far as I can tell, for some of these men are confirmed real, and are documented by the other people’s they raided/ruled over. Is there a reason to doubt the existence of such legendary figures beyond a popular trend of dismissing anything from legends? Similar to the beliefs that Troy and the Trojan war never existed or happened among 19th century historians?
People claiming legendary figures as ancestors for purposes of clout never gets old. More can always be said on the matter, if anyone would like to have a go at He Who Wears Fuzzy Pants; for the meantime, OP, we do have some previous threads that may be to your interest: