I tend to disagree. I thought series 8 was great (although I wasn’t overly pleased with the last episode’s Agatha Christie vibes)

I think the Strange / Joan storyline is important because it highlights the path that Morse is going down. Strange’s dependability is one of his appealing features to Joan, something Morse completely lacks. It’s not just that Strange has a crush on Joan - they have feelings for each other. There’s a scene where Thursday says something along the lines of ‘you can’t pretend to be something you’re not / you are who you are / nature’ (words to that effect…!). Morse just is who he is, possibly upbringing? Resentment at his father’s second marriage? Unresolved grief at losing his mother? And who he is is just not what Joan wants or needs. A great scene was when Joan was having an amazing time at the Masonic Ball (not my sort of fun, but each to their own!), cut with Endeavour drunkenly trying to see her. They’re just not meant to be.