That pretty much sums up American vs. British comedy (televisual anyway) for me.
US: 'momentarily interesting' (resp. funny at the time) - series of one-liners and the like; UK: character development, hard to explain why it's funny, might take 'getting into'.
Green Wing for example - I thought it was absolutely absurd when I first saw it, and it is. But for some reason I went back to it (or was made to) and stuck with it for a few episodes while I learnt to love it. And now I do, it's one of my all-time favourites. And of course I've been back (several times) to watch the first episode(s) again, and they're hilarious too.
Or perhaps a clearer example is the original UK The Office (Ricky Gervais) vs. the US version (Steve Carell). Same rough outline obviously, some of the same (especially early in the remake) storyline and jokes, but somehow even then the humour is very different.
(I'm not hating on the remake, I enjoyed it enough to watch it all once I accepted it's different, and stopped expecting 'The Office' as I knew it. Especially once it found its own path and diverged from the same jokes - IMO - worse delivered.)
I think it's less that the US doesn't have those, it's just that they have both types, and they also mix them. Seinfeld wouldn't have been half as good as it was without you knowing the character and how they would react to specific situations.
I think part of what you're identifying about first episodes is maybe a difference in style between the US and UK. A lot of UK comedy definitely seems like the characters are pre-baked into the writing and the actor is already mature in the role in the beginning, while in the US it feels like they've left the role a little hollow at first and allow the actors (and future writing) to evolve the role into what it will be. This can make the first episodes feel "off" when you go back to watch them, but I'm not sure it's necessarily a bad way to go if the goal is to find a really good character.
It's also possible that the UK network(s) are amenable to planned out entire seasons while the US networks are more accepting of buying a pilot of a few episodes and seeing where something goes, which would favor some of these approaches in each case.
I hope it's clear enough that I'm not disparaging US comedy. There's plenty of it I enjoy.
I think a key point I started making but didn't really conclude is that British comedies stay with me; I can quote them, accidentally fall into their characters like an eccentric myself, enjoy them without re-watching them. Monty Python; Fawlty Towers; Reggie Perrin; The Office; Green Wing; Dad's Army; et alia.
I think the closest I can come to that sort of absent enjoyment with US TV comedy is to imagine April Ludgate's (Parks & Recreation) face in reaction to something.
Maybe it's partly that US comedy veers more visual & slapstick? Certainly not all of it, there's very little in general, I commented on that in a recent thread on Airplane!, but that too is American of course. Though I'm not sure how well Fawlty Towers would work audio-only.
I think that's an example of what I'm saying. Rather than the characters being mostly realized by the writing, they let the characters and actors grow into specific parts together.
It's similar to movies. Special effects are momentarily interesting, but it's the plot that overwhelmingly matters.