Like the scaling and it make sense, we know Whitebeard reach his prime later.
In that case how I see the tiering during god valley:
Top top tier Xebec
High top tier Roger
High top tier Garp
High top tier Whitebeard
Mid top tier Big mom
Low top tier Kaido
Low top tier Shiki
I think Roger,Garp,Whitebeard hit the top top tier lvl few years later, I think Big mom hit high top tier also later.
Rocks, Roger and Garp were easily already solid high top tiers, no doubt.
Whitebeard and BM could have lacked awakening for all I know and Whitebeard might not have been as skilled in CoA as he was in the Flash back perhaps.
That's how I can see how Oda could make them all just be low top tiers.
Kaido probably was just a high high tier back then imo.
His base strength was probably lower than it is now and he did not have that "dragon scale" durability yet. He legit could have had the fight of his life against a guy like Katakuri under those circumstances.
Might honestly have been weaker than Hybrid Yamato is now.
Would also fit in with the fact that he was just an apprentice.
And going by the fact that he was highlighted together with BM and WB as that "monster trio", Shiki might legit have been just a high tier. He pretty much stands and falls with his devil fruit. If he did not have it back then, just like Kaido, he could likely have been the weakest.
All that combined would scale pretty well against two high top tiers + whatever they additionally had on their side.