The Flight Director dot was originally designed to facilitate a Mach 0.89 climb, as the most fuel-efficient way of getting the aircraft up to an operating height.
The Attitude Indicator FD took its computed feed from the Flight Control Computer, with inputs from the height and speed units (whose names I can't remember).
AI's were not all that reliable. Contrast them with the superbly engineered navigation system (analogue/barely digital!)