Is it as credible or accurate or even reliable when it comes to learning a thing or two about history?
No, no and no
I remember one of our proffessors called it "the Hitler channel" due to their fascination with the Nazis. But it has got even worse since then with ancient aliens and reality TV about pawnbroking (seems pretty random).
Most history on TV is quite bad today. There is more of it than there was 10 or even 20 years ago but a lot of it is dumbed down to such an extent the original message is completely lost or muddled.
The sort of golden age of history documentaries was probably 1960's-early 2000's. In the UK there were several landmark ones such as The Great War (1964), Civilisation (1969), A History of Britain (2000-2002), however these are getting pretty out of date now, especially The Great War and (Western) Civilisation. The old documentary format, effectively a historian standing in front of a camera for an hour didn't really bring in the viewing figures that TV execs would have liked.
Don't get me wrong, they do still make quality documentaries, but now they are going in more for entertainment with a lot of the new material. David Starkey usually pumps out a decent doc now and again. Then there was another one about the history of the crusades in the media on BBC, and if anyone can remember what it was called please comment as it was really interesting, it was either 2015 or 2016.
A history of media person would be better placed to fully answer this question.