Could be that Mihawk is even older, the oldest being in the show...
He might not be named Dracula for nothing, perhaps.
And then Oda will show that Shanks beat Loki fair and square, resetting all this supposed powercreep, showing that all legends are in the same ballpark as Loki.
Nah not necessarily.
I think Shanks combines a lot of special abilities, that no one else combines in that way: all kinds of advanced high end CoC tricks (mass, aura, wifi) which rules out everyone bar perhaps prime Roger, Joybody, Imu already + he has Gryphon. If he can fly with Gryphon or assimilate a hybrid form, similar to Ashura, it's likely an ability that no one else has aswell.
This chapter showed us how Loki is simply not beatable on the ground. Take away Omen's absurd firepower and Imu's wings- how is anyone supposed to handle Loki on the ground. I just don't see it tbh.
Shanks does not have to be >> Primebeard p4p, but he might just be a prime Roger that can fly and that might have done the job against a CoC unexperienced Loki.
All in all I'm sure that, if he beat him fair and square, it's something only he could do, besides Joyboy & Imu, , thanks to very specific conditions.