The comparison to Bunny Girl Senpai is a really, really good one actually since they do have an extremely similar storytelling structure. I watched that show+movie just recently, so it is fresh in my mind. I think the main thing that kept me engaged with Bunny Girl as opposed to Clannad is the characters. I really enjoyed the characters in Bunny Girl whereas in Clannad, whenever certain characters showed up (iirc, mainly the guy friend that keeps challenging a girl to a fight), I just found it annoying and took me out of it.

I think there is a lot you could compare/contrast between these two shows and it is making me think critically about what made one work for me and the other very much not work. Thanks for the food for thought!