There are significant design differences between the FL sizing die in a Lee set and the sizing options from Redding/ Whidden/ Forster, etc. Mainly the Lee set doesn't have a bushing option, but even then the high dollar sizing dies are going to be cut more precisely, with better finish, and have more options in terms of what you can get the internal dimensions cut to. The seating die is also fairly different in that it obviously lacks a micrometer stem adjustment, and also doesn't have a sliding body insert so alignment in the seating process isn't as precise. The collet neck sizer also has some interesting utilizations, but without a body die in the set you have to use the FL sizing die eventually so it's not a perfect solution to working necks less.
The FCD die is unique, invaluable, and I have one in most calibers I load for. ButterBean has a set of instructions on how to use it as a tuning step in the loading process.
Lee makes less expensive stuff. It's fine, it works, it makes loaded rounds. But you're asking what's the difference between a Ranger, F-150, and Super Duty by saying they're all trucks. They're built for different things, the question is do you need what the more expensive ones offer you? If you need to pull a 20,000# gooseneck the Ranger is going to tick you off and ultimately not be functional for you. If you're loading mixed headstamp pickup brass using a powder drop and Core Lokts it's not going to matter what die you use; the consistency of the die isn't the limiting factor in the quality of your load. If you use a Prometheus to put a charge into annealed Lapua cases and seat pointed Bergers over it all you don't want a poorly cut die to be what ****es away all the effort and cost you put in to get to that point.
Do you want to make some handloads to go pop a whitetail under a feeder at 50 yards with a 270? Or do you want to make first round hits at 1,500 yards? It's a spectrum, so pick where you fall along it.
