I think it's a clear case of Oda designing something in his mind at the beginning, but slowly changing his mind along the way
It's the whole "romance dawn" thing.
When Oda says these 3 were the initial catalysts, i dont think he was lying. I think Sanji's role grew way beyond what oda originally intended. But this change happened way WAY before TS.
The Kuma moment in TB, imo, is the moment when it actually should have hit everyone that Sanji was intended for more than "fight 3rd strongest enemy".
BUT, as the scene develops, we also see that Oda will NOT remove Zoro's role for Sanji entirely. So only Zoro takes the pain.
As far as importance goes for the EoS, Zoro will always have a single fight that will "set it apart" from sanji as far as notoriety goes: Mihawk.
Its why I believe, Luffy final bounty will be 5.6B, zoro will maybe be close to 4B, and sanji will be below 3B.
Not a power scaling thing, but notoriety. And relevancy.
Take also how Oda cooked some half baked kaido/King luffy/zoro parallel in onigashima.
How he usually puts beckmann closer to shanks than roux and yasopp.
It is fine.
I dont sanji to steal zoro's thunder. I am just happy that my fave gets a bigger role than one would expect at the beginning.