Nobody views Shanks as no 1 of all time. Most readers will tell you Garp, Roger and WB in their primes were stronger.
But when it comes to portrayal, feats etc there isn't one character on par with Shanks right now.
Wifi diff. 1 shot 3 billion berry Kid. Making marineford back down. Kaido's top 5.
And the narrative. Luffy still isn't strong enough to meet Shanks yet.
Oda couldn't have made it blatantly obvious Shanks is stronger than Akainu and most other yonko