BLACK LIGHTNING felt rushed toward the end. And they seemed to introduce Martin Proctor late in the game just to have a fall guy for the season. Yet he was a cardboard cutout nowhere near as well developed as the other villains.
I think 16 to 18 episodes is the ideal.
However, people act like filler stories are terrible, when I feel these are often the best stories. They aren’t serving the larger story arc, so they can try other things. And a longer season allows some of those epidodes.