So, I'll chime on this topic. If you watch the FD's pitch bar behavior beginning 0:09 in the video, you will see that as the pitch attitude increases from 0 (at 0:09) to 5 NU (0:12) you see that the FD pitch bar follows the pitch attitude increase. At 0:09, both the FD pitch command bar and the aircraft symbol pitch attitude is 0 NU. As pitch attitude was increased from 0 NU to 2.5 NU, the FD pitch bar followed it also to 2.5 NU. At about 3 NU in aircraft pitch attitude, the FD pitch bar stopped moving and following the pitch attitude increase of the aircraft symbol. This is not the correct behavior of the flight director system.
The FD command bars pitch and roll command are generated by the flight director compute relative to attitude changes required to satisfy lateral and vertical references, in this case displacement of the localizer and glideslope needles from the centered positions. The FD does care what the actual attitude of the aircraft is at any given time. in fact, you can change attitude of the aircraft in pitch and roll instantaneously away from the FD bars, those bars would not move. You can literally pitch up and down rapidly through the FD bars, and as long as you did not displace the localizer or glideslope needles from their centered position, the FD command bars will not move.
This movement of the FD bars with the changing aircraft pitch and roll attitude is a common mistake that I see in flight simulators (to that mean PC type, not the real Level D's). It makes using the FD difficult for PC pilots because they are not used to also watching the raw data, and then get into the habit of chasing the FD. The video is a very good illustration of this behavior.
In contrast, watch the FD roll bar commands for the same period from 0:09 to 0:12. The minute the roll begins, the FD roll bar begins moving back to the right. It does not follow the roll of the aircraft and await a localizer displacement before moving. In roll, the FD roll bar is behaving correctly. if the FD pitch bar were behaving the same way, when the increase in pitch attitude began at 0:09, the FD pitch bar would not have moved, but remained in the same pitch attitude calculated to satisfy the current displacement of the glideslope needle from the centered, on glidepath position.
Just to provide my background. 34 years flying business jets. 3 1/2 years teaching in the Learjet simulators. 17 years in Collins Proline series, and 13 years in the Proline 21. I have done these little tests in the Level C and D simulators, and in the real airplane. The FD pitch command bar and roll bars, or the "V" bar does not change with pilot-initiated pitch and roll changes. They only change, i.e., move in response to computed commands to satisfy the reference target.
On another note, I saw above the comment about flying pitch for speed and power for glide path. It is always for coordinate change of both. However, as a technique, in the Challenger 300/350 with its big, sailplane type wing, I have found it easier to trim for speed, i.e., VREF, and then make small thrust adjustments to follow the glideslope/glidepath. I don't use this technique as much on the Lear 75, which is more straight wing jet. But sometimes, you have to try other tricks.
I believe that if you tweak the flight director pitch command bar programming so that it does not follow pitch attitude changes, you will go far in addressing these concerns.
Just one pilot's view.
Thanks,
Rich