Loki has proven himself in feats and portrayal department though. Garling failed horribly.
Defeated weapon that not only Harald but NO other Giant for centuries had been able to handle.
Took out the man on par with Rocks, Harald, his father, when Harald had a power boost.
The entirety of Elbaph couldn't handle Loki.
So powerful Linlin WANTED HIM as a son as an actual ally, not a pawn.
Garling had aura (emphasis on HAD). Loki is that guy.
I think a lot of us looked more into "Oda won't let Shanks' dad be weak" and overlooked "wow Oda fucking hates the Celestial Dragons".
Garling is proof IMO that Oda is willing to break Shanks' wank when needed. Shanks gets gassed because he's that guy, Oda's fine making him look bad with Garling, and Barto.