Because his siblings get the abilities boosted by their RS. Again even without using boosters, the RS adds durability. More durability = Sanji being able to hit harder...hence all his attacks get stronger.
Again you are misunderstanding the point. I haven't argued that Zoro hasn't gotten stronger through his training. Him getting stronger through said training is irrelevant to the fact that he hasn't used his ultimate technique.
Again you are misunderstanding the point. I haven't argued that Zoro hasn't gotten stronger through his training. Him getting stronger through said training is irrelevant to the fact that he hasn't used his ultimate technique.
The technique doesn’t change. The damage might be different but the actual technique doesn’t change. Sanjis Diable Jambe isn’t related to his vinsmoke bloodline. So the suit isn’t going to work with that.
However, just like with Zoro, the technique won’t change but the damage will because of upgrades.
Any technique is strictly Sanji/Zoro and Sanji could use it without the suit and Zoro can use his with basic swords however, the damage the technique will do will change for both so to RS/Enma.