Sanji as a character is not someone that "will do anything for his ambition". His ambition will come from exploring the world, not from fights. Luffy and Zoro's dreams directly put them into confrontations.
The reason he fights, is to protect his friends. He does not think twice before jumping into an enemy attack to tank it and save someone else. Saving Usopp from Enel, going ALONE in the sea train to rescue Robin and Usopp, Taking Absalom hits so Nami wouldnt get hurt, charging against Kuma in rage after his friends started disappearing, even though he knew he had no chance, offering himself to Kuma, to protect the crew, even Zoro. Sacrificing himself going with Bege, saving Nami, Chopper and Brook there. Staying as a prisoner during Whole Cake to protect Zeff. Throwing everything away by relentlessly kicking his captain in the face, and telling the woman he most simps for to "stfu", so they could leave alive, while he would be the sacrifical lamb.
Even though, friendship is a theme for ALL the SH's, it is more flashed out for some, than it is for others.
Even if Sanji is strong, it's not his "thing" being THE strong character. That's more Luffy and Zoro area. That's why they constantly have moments to shine in combat, meanwhile Sanji have fewer, but it does not mean the character can't keep up with others. If Oda wants Sanji to solidify himself back to the fanbase as the third member of the monster trio, by using the Raid Suit, Oda will simply do it. He won't have Sanji going special training or whatever. The Raid Suit exists to replace all that, because the "i'm going to train and get strong" it's not his theme. Its Luffy and Zoro's.
And the "gap" between Zoro and Sanji only started to show from Punk Hazard onward.
Until Fishman Island, the M3 dynamic was exactly the same as it was before TimeSkip.