Like other users (for example, here and here), I’ve found legato playback in Dorico somewhat problematic, and requiring perhaps more engineering than it should.
The latest annoyance is Dorico’s handling of these few notes in Schönberg’s Fünf Orchesterstücke, the first movement of which I’m currently entering into the application:
https://stash.miloonline.net/dorico/schoenberg_playback_yuck.mp4
Notice that, for some reason, when the notes are slurred, Dorico interprets the second note’s duration as longer than short. That’s what the Playing Techniques lane shows, anyway.
Originally, I was disinclined to fault Dorico for the poor playback with the slur present (thinking that Spitfire was probably the real culprit), but when I watch my VST, it switches to my “short” sample for the second note regardless of whether the slur is present. So now, I’m just confused as to what Dorico is doing, and I suspect that it’s actively involved in screwing up the playback.