It’s treated identically to Shiryu and the raid suit. Even oda made it the same as shiryus and raid suits.
Chill.
You are derailing from what it is.
It's not "true invisibility" as the raid suit and shiryu. Even Queen says it is different.
Sanji's invisibility comes from how fast he moves.
NOW, what this means, and from what Oda doubled down on the SBS, is that Sanji's full speed is unmatched by any other character that we've seen so far. The only exception being Kizaru because, well, "discount light speed". and maybe, MAYBE Enel.
Sanji's speed is in such a state, that, in order to set it apart from other fast characters, Oda decided to use the same SFX as the true invisibility characters. That's the key here.
The issue is, arguing that current Sanji doesn't have "top tier speed" is plain stupid.
But, alas, Sanji suffers from the Speedster curse that every other speedster does. PIS.
Otherwise he would simply be too broken. Like the Flash, same issue.
That's all there is to it.