The issue here is that Oda could have easily said "his strength surpasses that of Red Haired Shanks." There is absolutely nothing stopping Oda from writing that, if that is the message he wants to convey.
Like what author in there right mind would sit down and think to themselves "I am going to write his Swordsmanship surpasses Shanks, but everyone knows I am talking about strength." That doesn't even make any sense.
Personally, I don't care which one is stronger, but we can't sit here and just pretend the author means something completely different than what he wrote, just because. No need for such ambiguity, if the message is meant to be clear.