Thank you, Mr Gerard, for explaining the difference between PPro and AE.
Perhaps just a thought ... would the following scenario be sound?
>> Although AE was designed for pixel-level calculations, perhaps it can somehow determine that a layer-segment has not been changed? such as a freshly-imported movie or a newly-pre-rendered movie (which is meant to be a completed segment of a project). For pure (no changes) footage-segments, perhaps AE can invoke the media-player engine instead of attempting to re-calculate every pixel? AE can always revert to pixel-level calculations when it reaches any changed/effects-applied segment.
I agree that AE is a great tool. But unless all short sequences can be completed in single sessions, AE's current design means that everything need to be re-calculated and re-cached the next time we open the same partially-completed project. If any segment can simply be played (media player), it seems an overkill to re-calculate and re-cache every pixel, which consumes resources that can otherwise be used to serve those other segments that have indeed been changed (and/or have any effects applied).
Just my five cents' worth from an amateur hobbyist's view.