Well, I don't know about "fiddle", but you do have to get the wheels on the tracks, I agree. However, it's not like the tiny stuff, it's typically pretty easy to get all the wheels on and be ready to go.
I'll admit, there are a few locomotives like the DC3 Inspection Car and the Baldwin Centipedes that take a bit more effort to get all the wheels on the track correctly, but it's not like it's that difficult.