I see what you mean with the trombone sample.
I've used MIDI in similar ways where I just need (say) a quick bass run into the chorus.

And as Peter and SaxaBruce mentioned, using either or both seems to be a viable option.
So your heading "Are RealTracks Killing MIDI" are a great starting point for discussion.
Those who are newer BIAB users, and have ONLY used RTs, may get intrigued enough to
check out the possibilities of:

- seeing what MIDI is all about

and/or

- seeing what Playable RTs are all about.

LLOYD S