No worries, I am not getting into "Luffy saying that he needs Zoro to defeat swordmasters". With all the differing translations we can barely tell which one translates correctly, at least as close as it can get to its original meaning in Japanese. Whether Luffy said that or not, I dont know but from what I can see, he actually does need Zoro to deal with swordmasters instead of him dealing with them.
The OP history simply backs it up. Oda writes the story to fit Luffy so that he doesnt need to on swordsmen, very convenient that each enemy has 1 swordmaster in his ranks. When you compare current enemies there is always one master swordsman which Luffy doesnt have to deal with because Zoro takes him on, however, look at the old generation, look how many swordsmen there are.
Roger and Rayleigh in the same crew, good luck not having to deal with swordman. Rocks and Shiki in same crew, again 2 swordsmen. In Shanks' crew there are at least 3 master swordsmen it seems and conveniently Luffy will never have a serious fight against them. It just works splendidly in Luffy's favor so he never has to take on a master swordsman. Everything is designed to fit Luffy's needs.