I can understand that point of view. Then again, they call it “conventional wisdom” for a good reason.
Yes, because it's not the same thing as genuine wisdom. It refers to the widely-held beliefs that shape people's decisions -- regardless of whether those beliefs are objectively true. There have been many cases where unconventional ideas turn out to be the truth.
I think the reason TV networks and studios favor the 100-episode sweet spot is because it's traditionally believed to be necessary, but there are numerous exceptions. Lots of shows have done well in syndication with fewer episodes.
Sadly, I haven’t had the opportunity to study Star Trek’s particular case, but if you will notice, the show isn’t exactly in continual, permanent reruns.
Not in the 21st-century media landscape, where reruns of old shows in general are less common due to the competition from DVD sets, and due to cheap reality programming and infomercials dominating so much airtime these days, even more than in the past. But I'm talking about the 1970s, the formative years of Trek fandom. A large part of what made Star Trek
such a huge hit in the first place, after getting only mediocre ratings in its first run, was the fact that, back then when syndicated reruns were more of a television staple, ST was
, in fact, in continual, permanent reruns for decades
. Throughout the '70s and '80s and probably into the '90s, there was never a time when TOS wasn't in reruns somewhere. It was ubiquitous, and that gave it a much greater popularity than it had previously had. And the fact that people saw the same episodes so often, really got to know them and connect with them and memorize their titles and dialogue and worldbuilding details and music and so forth, contributed to the devotion of Trek fans, the commitment to detail and minutiae, and a lot of what came to define Trek and SF/fantasy fandom.
Additionally, The Next Generation, Deep Space 9, and Voyager all share a similar fate; they run from time to time, but not continually, year-after-year.
And not to put too fine a point on it, look at Fringe. The show ran four seasons, to about eighty-or-so episodes, and was renewed for just enough of a final season to make it rerunable. In fact, Science Channel here in the U.S. of A. just picked it up to go into reruns even though its initial run hasn’t yet completed.
Again, the media climate is completely different these days. Syndicated reruns are such a minor factor in television now, compared to DVD sets and streaming online video and the like, that I find it rather bizarre that the "conventional wisdom" of the 100-episode target for syndication still has any real impact on the decision-making behind TV shows. I could see it being an issue 15 or 20 years ago, but as you say, reruns don't happen as often anymore, so it doesn't seem as relevant. That's another drawback of "conventional wisdom" -- it's not necessarily reflective of new truths.