This has turned out to be quite the thread for showing that if I believe principle A, then principle B can never apply, instead of applying some conflatory logic.
If you were able to magically remove a main rotor head and blades spinning at full speed and then even more magically transport it into a perfect vacuum, if you instantly applied a force to the spin axis, the apparent movement would indeed appear somewhere around 90 degrees later, just like a gyro. But if you then evacuated the vacuum surrounded the spinning assembly with normal atmosphere and tried the same experiment, you would get a different result because of the aerodynamic interaction. If then instead of a mysterious and magical force being applied at the spin axis, you tried to replicate the movement by cyclically changing the pitch of the blades, you would see that same 78 degree lag (or whatever!) before the effect of the input becomes apparent, because the aerodynamic effect is the predominant force.
Gyroscopic principles assume a solid disc, which is clearly not the case with an MRH and blades, but that doesn't mean gyroscopic effects are not felt. When you lift a tail wheel aircraft during take off, part of that yawing action you have to counteract is gyroscopic effect (along with engine torque, slipstream and P-factor). Just because the predominant force is aerodynamically derived, it doesn't mean gyroscopic forces aren't present. Instructional text books often pick on a common and easily accepted view, even if it's not the complete story. There's nothing wrong with that, as long as the critical principles of flight are understood. Gyroscopic principles are a massively complex area in themselves, so no need to complicate the explanation of what is the predominant force is with another far more complex area which is a secondary effect.
Things don't work in nature and science through picking only the simplest explanation, but it's fine to use that to illustrate a general principle. Strangely enough, thanks to some very smart design engineers, I never once had to think "better start banking early here, just in case that 78 degree lag doesn't work. Wherever I moved the cyclic, the aircraft magically followed. Good job design team!