Yes.
1)the title didnt exist so he was able to clutch it without specific parameters.
2)the majority of the road glyphs at the time dont seem to be held by emporer level pirates. Which brings me to 3.
3) were there any emporer level pirates when roger was a rookie? Who were the pirates 30+ years older than roger when he sailed?
4) were sengoku, garp, and kong the only marine heavy hitters? No warlords, pacifista, seraphim?
5) who were his rivals down to the number? Sure, whitebeard was his equal, but who on WB side took on Rayleigh and gaban? Or later on, oden?