-It was a theory that someone that resembles Shanks' face give him a scar
-We though it was Roger even though he's not Shanks alike (Ace had more reason in that departament and WB never brought that up)
-It was revelaed 800 chapters later that there was in fact, a character that looked exactly like Shanks in the past, and he was in GV too with WB. So we put 2 and 2 together.
It was very razonable, nothing crazy!
Yeah, but it has alwasy ahd plenty of flaws.
1) it was clear - we all agree - that back then Oda meant Roger. So know, being Garling, would have been a retcon of what Oda intended to be. OK;
2) in Oden's FB, much closer to Garling's introduction, WB didn't have any scar on his chest. Instead, he had a band aid on after the fight against Roger. Now, not only this checks with whom Oda intended to be (Roger), but making Garling the one would mean a second retcon since, as said, he didn't have any scar during Oden's FB, ten years after GV;
3) WB should have understood Shanks was Garling's son, which is unlikely considering he didn't recognize Ace was Roger's son.
To me, it has always seemed very problematic. Sure, Oda can do anything, but still.