S1 was a normal length season so you've just invalidated your own argument.season 1 was the best because it had a plan, a beginning middle and end.
Not at all. What matters isn't the length, what matters is having a goal in mind.
The argument I was debating was the one I see bandied around a lot - that 13 episode seasons are somehow automatically better than longer ones. Never seen any evidence of that. Why should a staff of writers be capable of writing X number of good episodes per year vs. X + Y number of episodes? If the writers are overworked, hire more writers. With more episodes, you can afford a larger staff.
Having a goal in mind doesn't inherently have anything to do with length. And unlike length of the season, which I think is trivial, having a goal is a very useful idea (though not absolutely necessary).
The reason subsequent seasons fell apart is that they were artificially continuing character arcs that were never meant to continue past the first season
The solution to that is for the writers to recognize which characters have potential for extending their character arcs and which are hopeless. Focus on the former, kill off the latter.