Sanji is strong but not enough here :
Scenario 1 Luffy doesnt have advanced observation or armament : still without advanced Observation, like seeing future for seconds, he can sense Sanji while being invisible or react by instinct. For me, invisibility is not a factor against Luffy. With classic armament, I think it's a hard battle if I discount G4 as well. Both have speed, and I still can think Luffy's Gear 2nde a match for Sanji's, and their strength can be around with Sanji's suit. But still, I see Luffy having more stamina and durability. If we take Luffy without G4 and current enhanced abilities, I can see Luffy winning high diff. If we take any forms of G4, it's no more a contest as Luffy easily crushes him in one or few punches.
Scenario 2 Luffy has advanced haki but no gear 4th : the gap is even higher here than G4 (previous enhance) vs Sanji. He can see Future for instant so can anticipate Sanji's move and give Luffy even better mobility to his upper-match speed. If we take current Armament, I can see Luffy KO Sanji in one punch, as he could hurt Kaido in chapter 1000 in base form with internal Haki while he couldn't in G4 (previous enhance) when Kaido was drunk. With current Haoshoku inside internal Haki explosion, his damage are far more heavy than previous G4 used against Doffy, Katakuri or Kaido's first fight. Luffy easy win here.
For me, even with his suit that enhance his abilities, Sanji currently remains the 4th in the screw. Zoro is 2nde to current Luffy, Jinbe is third with experience, strength and durability. But Sanji can grow higher than Jinbe in Future.
I think a fight Sanji vs Jinbe should be more interesting than this current one.
