I dont think Marvel 'need' to restrict their casting choices to actors that have that 'quality', which is what you seem to be intimating (if I wanted to be pedantic I'd highlight that theres no requirement for Strange to look Mediterranean given that [although born in Philly] he actually comes from Nebraska, with no mention of Italian, Spanish or [given other casting suggestions on here] Mexican roots).
Visually, all thats basically required of an actor to play Strange is dark hair and a moustache/beard/goatee, and even those things can be done in makeup. As I said, the casting net for Stange can generally be wider than most lead comic book characters.