Playing and rendering SWF files is super slow and it should match the performance of that of shape, vector and video file footage playback when played as apart of a composition's timeline. Even matching/relative speed as Animate's sluggish timeline playback would be of benefit.

This has been tested with continuous rasterising on and off at resolutions between 1080p and 4k. No effects were applied. Also tried both software and hardware rendering (already known lack of support).

I can check that "optimise for After Effects" button all I want, it doesn't fix the playback speed issue. I just feel that Animate>AE uses haven't been fully thought through much like dynamic link has been and anyone working with files from Animate need to really overthink how it's going to work once imported into AE.