It's clear as day that Luffy/Zoro is going through haki development while sanji's path to surpassing limit is linked with Lineage factor.
He isn't getting AdCoC. That won't go with his character portrayal nor with how oda consistently didn't even show sanji with clear armament coating when he has done so with others.
So, oda is taking the route of altering Sanji lineage factor
We know that DFs can alter lineage factor and that's how one gain abilities
If we go back to first arc of NW - PH, we encountered artificial dfs which also alter Lineage factor but it works with zoan df only so far.
In WCI - we have RS (physical inhumane attributes)
In wano - we have Smiles
And, few chapters back we got this
Sanji - got healed from broken bones, became more durable and the enhanced physical strength.
One of the thing which is common in all these arcs is - Technology + Zoan df attributes
In above image, Queen outrightly said that's its not haki.
So, if we link everything then it's becoming evident that Sanji is witnessing Zoan - like transformation - like he poses some sort of devil fruit which can transform him
Perhaps this was what foreshadowed by oda during TB - transformation like a zoan df user but with element of fire.
Just look at sanji's face here - it appears he is transforming which again makes me feel that sanji PU will give him zoan like attributes with element of fire.
As far as yamato is concerned, then a lot depends on how much growth Sanji will show.
But one thing is certain, Sanji will grow stronger than yamato sooner or later and oda will continue to give him 3rd strongest opponent.
