I have unchecked “Improvise note attack and release” (tried on every voice) but whomever sings still scoops into and slides out of notes and glides all over like a pop star. I’m tying to get as flat (unmodified) a pitch performance as possible for a choral piece.
Sing mode is automatically generating pitch curves for each note.
Enable Manual pitch mode for the notes you want “pitch-snapped” and then remove the pitch deviations from the Parameters panel.
If the transitions are still too smooth, set the transition sliders to zero in the Note Properties panel (these sliders are only visible when Manual pitch mode is being used).
If you find this is too strictly adherent to the notes, you can also try to still use Sing mode and make the curves less “lead vocal”-like by:
- reducing the Expressiveness slider in AI Retakes
- reducing the Vibrato Modulation slider in Note Properties
Thank you! This of course could have been solved by me just RTFM 
but I appreciate it.