The issue is that Sanji will not be a Top 3 combatant when the Strawhats challenge the Marines/World Government.
We'll have:
- Luffy
- Zoro
- Sabo (?)
- Yamato
- Law
- Kidd (???)
The above six are all going to be decently stronger than Sanji at EOS, and at least 3 are guaranteed (Luffy, Zoro and Law), with another 2 being very likely (Yamato and Sabo).
If Sanji is #6 or #7 on the Alliance's side, how on Earth is he getting a solo fight vs an Admiral?
Looking at it from another angle, Luffy will be fighting Sakazuki; can you really imagine Sanji defeating someone on the same level as Luffy's arc opponent? After his performance in the New World?