The first season is pretty bad, but necessary to set up the various arcs.
Season 4 crammed the final two major plot arcs into it because they thought they were getting cancelled. But then they didn’t. Season 5 is almost entirely filler.
In fact, once you finish Season 4, I’d recommend jumping right to the series finale (last episode of S5) and watching that. Then watch Season 5 from the beginning and think of it as a spin-off show that didn’t go anywhere.
This was how I went through my last rewatch of the series a few years ago and it was perfect.
It’s a single PBS affiliate station.
A cause of concern, yes, but also a sensationalist headline.