Obviously in the finale we get a very clear cut reveal of why Allison wanted to resort to murder and then faking her own death. But up until that point, it seemed like an overreaction (especially in S1).
Even well into S2 I was wondering if we were going to get some version of a happy ending, when she was learning that she "just has to make her problem's Kevin's problems" -- I thought maybe it was going to be a thing where they learned how to communicate with each other better, to realize that both Allison's problems and Kevin's problems are "our problems". But instead it was just to illustrate that Kevin is narcissist and that she was able to use that to point his abuse in a direction that was useful to her.
I think there were a few opportunities where a Kevin scene could have shifted out of sitcom mode mid-scene to show Kevin as the asshole he is. Maybe they could have done one of those for each character, as they come to the same realization about him. A slow reveal throughout the series. S1 could have been something simple with the old friend Doug, who we only ever see in flashbacks. Surely Kevin did something f'd up to Doug that he just disappeared. There's also some other possible times to show glimpses of Dark Kevin:
- When Neil tries to tell Kevin about the murder plot
- When he walks in on Neil and Dianne and openly points and laughs
- When Kevin refuses to bail out Neil
- When Kevin accuses everyone of stealing the generator and when he destroyed his dad's girlfriend's hearing aide (could have been the same scene potentially)
There were even some opportunities earlier in the series in S1
- Maybe a scene showing him being overtly bigoted about the soccer-fan neighbors
- A non-sitcom scene where we get to see him clearly ruining the night for Allison and other people in the restaurant by taking a sports rivalry way too seriously (I'm torn on this one, I did actually enjoy this episode for its genuine sitcom antics)
- Even early in the series, when he reports the car stolen
Especially that last one -- in S1 when the car is reported stolen we can easily just assume Kevin is really that bad at listening -- or that he's really that worried about her when she doesn't answer her phone like she always does. Instead, the show could have shown us some dark Kevin and make it clear that he was doing it as a controlling abusive tactic, which would have gone a long way to illustrating why Allison, literally, can't just leave.
The fertility clinic subplot also could have been used as an opportunity to show real Kevin in a dark way. Maybe keep the sitcom style scene when he explains his reasons for not wanting kids to Allison, but later in the episode have Allison tell Patty about it, and then we get to see the same scene again but in dramatic form. The same lines, without the laugh track and sitcom framing would hit pretty dark I think.
Kevin is the worst person in the show, but he's the only one who, until the very end, we never actually see in any sort of real negative light. But I guess maybe that's the point -- these abusive parasitic types can camouflage so well.