The first two series of the Stargate SG-1 & Stargate Atlantis followed what Big Finish loosely call the "chronicles" style of storytelling - one series cast member narrating/performing a story, with a guest star actor supporting them. They've done this with their Doctor Who, Blake's 7 and Judge Dredd audios too.
It's partly a way to keep production costs down - cheaper to get one actor than a whole cast! - and also lets you get around the issue of cast members who are unavailable (or sometimes passed on). These are usually a hybrid style of performance with some narrated story and some in radio play format.
Which is exactly what we did with the 3rd and final series of Stargate audios! We got two main cast members to play their roles and populated the rest of the series with new actors in supporting roles.
The problem with doing audio versions of shows with big ensemble casts is that things can get unwieldy with too many voices. I've always thought audio works best when the cast is smaller and more focused...
As someone with a lot of experience in writing and listening to audio drama, I have to disagree.
Your definition lacks nuance; if it's a text being read from a pre-existing work - like, for example Robert Petkoff's recent reading of my Discovery novel - that's an audiobook. The Sulu stories are clearly performances that were written specifically for audio and make full use of the medium to dramatic effect. The fact that the characters don't directly interact is irrelevant.
