Having used both MuseScore and Reaper in my workflow, I initially agree that scoring and DAWs are two different things, and that I could simply export MIDI files from the notation software then take let the DAW do the rest.

But I see the point of how good playback can affect the composition process, something notation software is not known for. Although I believe instrument quality should not be a cover up for bad compositions, there are undeniable instances where otherwise good compositions sound bland or uninspiring when played by the "lightweight" sounds bundled with notation software (as they are not DAWs). At times, after hearing it sound right within the DAW, with my favorite plugins and sound libraries, I am inspired to tweak the composition a bit, via the piano roll.

In such scenario, if playback could be improved, it would be nice if a DAW can be removed from the compose-listen-tweak loop. At the very least, have realistic instruments and realistic (humanized) playing, even before moving work into the DAW.