But I think the ideal season length is probably around 15-18 episodes. That gives you enough episodes to have some variety and breaks from the main plot, but isn't so much that the writers end up spinning their wheels, and still gives enough room to tell a good season-long arc.
17 Episodes feels like the perfect # of Eps per Season.
Given that 1 week of the year (X-mas / New Years) is going to not have any real new content.
Splitting up the Year into 3x Seasons with 17 eps each can give you the balance between "Too Long" at 21-26 eps per year to "Too Short" (5-13) eps per year.
And if you really want, just add in a double length Season Premiere & Season Finale ep where you have an actual 2 Hrs of Primary Show Content to Book End the Season's content.
And keep the 1 actual Hr of content per ep, I really enjoy the slightly longer than 45 mins setup.
1 true Hour of Primary TV Episode Content per standard episode length is nice.
Then you can stack in (Last Time Segment, Prologue, Show Opening Intro, <Primary 1 Hr Content>, End Credits, Epilogue, Next Time Segment)
That should get you to 1 hr, 10-15 minutes depending on how you arrange everything and that allows you space for commercials in a 1.5 Hr regular Broadcast TV time span.
Longer seasons work better for episodic shows, or even those that combine arc and standalones, like SUPEENATURAL. Shorter seasons definitely work best with arc based shows.
Supernatural & "The Flash" likes to mix in arbitrary Arc lengths for certain Arc based or Multi-Ep stories.
So they have plenty of Stand-Alone Episodes, Arc focused episodes, and multi-Ep Arc stories.
You're not locked into 1x Long Arc Length Season.