SHIKI LITERALLY TELL WB "the wall before us has fallen, now it's your time to reign " when talking about Roger's death
Shiki and WB knew who was the strongest. That's why that era is called Roger's era
Shanks wasn't top 1 or even top 2. Roger was top 1. People compared top tiers to Roger. He was the benchmark
Shanks on the other hand isn't the benchmark for power.
Failed Roger
He also lacks VoAT
Yes, because Roger was powerful 1 on 1, had a powerful crew, conquered the Grand Line and reached Laughtale. Hence it was his era.
Shanks was Roger's golden boy, Buggy who was on Roger's ship as well was certain that Shanks is the one capable of achieving what Roger did, but Shanks specifically postponed his endeavour to become PK, in the end sacrificing his arm for the new era.
Shanks btw. doesn't need to be the strongest. It is enough for him to be close. He can already go toe to toe with the strongest, while also having the strongest crew and the strongest allies (e.g. giants), allies that deeply love and admire him, unlike the allies of other Yonko, e.g. the Wano Samurai being driven by fear and resentment towards Kaido, hence not being fully loyal. Bro can even walk in and out of Marijoa and fuck over the WG by stealing the Nika fruit and feeding it to a boy he inspired to be PK, without consequences.