Doesn't work that way, Luffy,Zoro > SNs which didn't go through extreme battles (the majority of them), which Rayleigh said is the best training to Luffy. Kidd and Killer did so numerous times, Law has a broken DF and is a mastermind.
So no. Luffy and Zoro ain't stronger than these 3, they're fighting side by side cause they are on the same level.
Law got destroyed over and over by Doffy. He nearly lost his arm. Luffy beat Doffy.
Kid lost his arm and got his face fucked up by Shanks or Benny.
Killer got stigmatized, brutalized, traumatized and all the horrible things that ends with "zed".
Again, there is a difference between going through extreme fights and getting just beat up. How can you improve your strength when you actually lose a part of your body? or eat a smile?
This tells us why 2 years of training was necessary so that shit won't happen to the ST.
They are fighting with them for the moment. But I expect them to fall eventually or it's just bad writing.
The last two characters standing should be Zoro and Luffy.