I wasn't ready for a 28 episode sustained descent into darkness
I look at you, and I see the person I was three years ago. The explorer that my father wanted me to be. I lost something out there, and I don't know how to get it back.
This one hit me hard after everything that happened.
I see this a lot which is wild to me because I feel like S4 felt like it finally was real Star Trek but just rushed and some of the damage to some characters couldn't be fixed. All the major plot points that make Enterprise relevant to Star Trek happen in S4.
I'm curious where you put Discovery? That is the one I struggle the most with. My primary issue there is that for me I have to actually like and want to be invested in a character but as far as I'm concerned 10 episodes in to Discovery if the ship blew up all hands lost the Federation I can't think of anyone I'd feel sad for. Enterprise though has Trip and Phlox who are S tier, a few fantastic guest stars, and no character that is bottom bin material to me no matter how much fanfic quality writing they tried to force on T'Pol.
I really enjoy season 4 (except These Are The Voyages... lets not talk about that.) but I think it's definitely fair to say that the sheer adrenaline ride that was season 3 slows down a bit after the Xindi threat is resolved. You end up with a lot of these standalone arcs that, like you said, are focused on building connections with existing Trek (the augment trilogy leading into Affliction/Divergence is a good example) or arcs designed to set up the founding of the UFP. It's clear that they were also leading into the Romulan war which was only ever mentioned in passing in TOS. In that context I think the slightly slower tempo season 4 would have made an excellent breather between the two.
I am needing to rewatch Discovery, it was next on my list, but I got derailed when I couldn't even finish Enterprise.
I remember finding the concept of the ship to be ridiculous and irritating. So who knows, it may end up rating lower than Enterprise on my list assuming I can get through that one.
I really liked Phlox in the first episode, but never felt the followup was there.
As for Discovery, Saru is great, and he has a wonderful relationship towards the end. Michael is OK. Perhaps the show's biggest problem is that it has a big cast, but it never puts in the effort to develop those characters before it expects you to care at some chosen moment.
I've given it a decent amount of thought and it's fairly hard to pinpoint. I think it's just a general failure to create interesting characters and plot lines. It doesn't have the same optimistic and fun feeling that many Treks do. The intro is specifically awful.