That’s a big statement, Shiki was a true rival to him who can 1v2 Garp and Sengoku. Even Shiki shared the same sentiment as Sengoku. He thought that there was no way in hell that the marines will catch Roger. You know, the same marines that have Garp (who is really shaping up to be Roger’s true equal btw). Shiki also said that the era is WB’s for the taking after Roger died. Roger having that much of an impact on Shiki means that the latter logically witnessed something that separates Roger from the rest. Shiki seeing Roger go all-out in God’s Valley is the first thing that comes to mind. Kaido is also a might is right kind of guy, and Roger was the first guy that he thought of.