You're not wrong - it shouldn't be this hard.
My problem with everyone's solution about the guides is that very few curves turn exactly 90 degrees or 180 degrees, so now you're trying to mesh two guides together if you're going for some other angle (set one for each end of the curve and get points to line up? good luck)
My problem with FT pieces is they're just like model railroad fixed pieces - there's no easement into the curve... One moment you're going straight, the next moment you're immediately curved. Imagine trying to do this with your car - if your steering wheel instantly turned 20 degrees to the right your front wheels would skid before your car finally turned... You "ease" into curves by turning the wheel over time, railroads do the same thing - tracks ease into the curve by going from straight tangent (essentially an infinite radius) to a definite radius over a distance. FT goes to that radius immediately.
Trainz default drawing of curved splines does the exact opposite of this - even if you straighten the track leading to the curve, it goes from an infinite radius (the straightened track) to an almost instantly small radius, gradually easing out to a larger radius, and then back to a small radius before the next spline point. This happens with every spline point. The more spline points you add to the curve, you're not really fixing this, you're just adding more points for the system to calculate a curve to approximate the real thing, but no matter how many you add, the point is the spline curve calculation in Trainz is still following the same flawed procedure.
Barring a major overhaul in this calculation method in the core of Trainz, which would ultimately break thousands of existing routes because of the numerous current workaround methods mentioned in this and other threads, there is no perfect answer to lay curves correctly. As I've primarily worked on real-world routes, I just do my best to follow the track curves using UTM tile images (from TransDEM) and a lot of trial and error to get the curves looking right. Sometimes it's moving the "start" of a curve back into the straight section more, sometimes its adding more points to the curve, sometimes it's straightening or unstraightening track, regardless, it's a mess.
There's pros and cons to every piece of software... I find Trainz Surveyor a hundred times easier to work with than the World Editor in Train Simulator (which has never really been changed since it was Rail Works 2) and even though laying curves is more.... engineered, for lack of a better term.... in the RW editor, it's still a royal pain in the butt. It does draw curves more correctly, but figuring out where to start your curves when trying to follow a real world route using the horribly antiquated Google Earth overlay system is just as hard as trying to lay extra spline points in Trainz to do the same thing.