Right, I am exactly saying that. People take Pelt just for Swashbuckling and Guardian. People take Highlander just for… well, nobody takes Highlander. People take Hoplite just for Finestra and Spear Lunge. People take Barbarian because there’s no other option for a 2h sword build (other classes locked to spears or shields) until Highlander gets buffed.
There are a few exceptions and those are classes that are strictly unique. Priest->Chaplain is basically a 4-circle class, Quarrel Shooter is the only true autoattack build, and Psychokino is just broken in PVP. So those are low rank core builds because they all have an incomparable niche.
For the majority of cases you’re picking classes to fill in later. You go Linker or Cryo3 because you’re going Chrono and you might as well build full support. This is why Pyro is so painfully unpopular, because if you’re going DPS it makes no sense not to go Wizard3 - because investing in a low rank DPS class when you have Elementalist, Necro, Featherfoot, Warlock later makes no sense compared to boosting later classes by 50%. It can work if you want to go for a hybrid build instead, say Pyro3 Chrono3, but that just means you’re an awkward slot in parties that doesn’t fully fulfill any particular role.
So other than the 3 exceptions I named I can’t really think of any popular build where the core of the build is a low rank class.