Eh 50/50 what you're saying is not wrong but not entirely true either. For example back in EL Oda could have easily given sanji a guy with 1500 doriki, the dynamic would have remained but he chose to give him a guy 20 doriki away from zoro. The actual trio dynamic is not just about sanji being the 3rd strongest its actually referring to the "gaps" between these members, if sanji is weaker than zoro by a similar margin that franky is weaker than sanji for example then what are the requirements for the monster title, we can just add franky into the mix then. The actual dynamic is that these 3 are close, as unbelievable as it may seem that is the dynamic not equal but relative. How sanji preforms in comparison to luffy and zoro is what is important not how he compares to the rest of the crew for the monster trio dynamic to stay intact.