Remember when Jerry was the only person who wasn't okay with his parents' bizarre cuckoldry relationship with Jacob? Or when he was the only family member who wasn't okay with Rick constantly taking Morty out on adventures because it was causing him to fail school? He felt a lot more relatable in the first season because he was pretty much the only normal person.
Jerry had his moments of being a pathetic loser in season 1, but they were never in your face. One of the best episodes of season 1 was the simulation episode where Jerry didn't realize he was in a simulation, and the best day of his life wasn't real. Even then, it wasn't really at his expense, and the ending was treated as somewhat tragic when he realizes none of it was real.
But as the series went on, what started as a back and forth between Rick and Jerry became disproportionately shifted towards Rick. One of the worst moments for me is when Jerry points out that Rick took his family away, but then Rick retorts that Jerry knocked up Beth and "ruined her future" or some shit (ignoring the episode where it reveals their lives suck without each other). And Jerry weakly submits to the argument, despite him having more of a spine in the first season.
Jerry was the only character who stood up to Rick, and that's what made him interesting in the first season. But then they started treating that as a bad thing, roughly around the time Rick became an obvious self-insert for Harmon.
Jerry being a butt monkey could get grating, I agree, but it actually could have been made into something. What really stuck out as odd to me in season 3 is how all the characters in the show were slowly coming to terms with their lot in life, their flaws, and actually finding more healthy ways of coping with said flaws.
Morty, as a result of the previous seasons, is done being "a Morty" and is very obviously smarter, sharper, and more confident as a result. He sees through Rick's bullshit facades enough to know how to call him out on it and be ahead of him occasionally, but he's still innocent enough to have a good moral code whilst still be capable of being deceived by Rick.
Summer inherited all of Rick's ego and zest for adventure, but she had none of the stomach or wit for it. She mellows out and becomes somewhat coy about the people around her, but in this regard, she's adapted to Rick's shenanigans the best in the family and is openly accepting of the weird which is in contrast to how bitchy and afraid she was any time she got a taste of what Morty used to have to put up with.
Jerry began to realize that he didn't have to compete with Rick to be a good person. His solo episode with Rick, while initially demeaning of Jerry, ends with him coming to the realization that he should man up and stop fighting to be against Rick and more to be someone that isn't Rick. (Which is funny considering alternate realities of Jerry tend to be super far better off than other characters in the show.)
Beth got knocked down a peg and realized that her family is exactly what she deserves, and that she shouldn't idolize an almost entire stranger in Rick.
See they had all this unintentional growth thanks to Rick being around, you expect that the show is going to capitalize on this and make the ending of the 3rd season about all these characters, in their own roundabout way, becoming smarter than Rick in that they found healthier ways to deal with their lives than Rick who continues to dilute his pain and run away from just about every confrontation.
INSTEAD we got a finale focused on the President, a half-assed conclusion to the divorce sub-plot, Rick continues to be unstoppably right, and the ending is just a way to return things to the status-quo, something the characters even
directly fucking say to the audience's face.
Like, ok, you got me Harmon. I didn't expect any of that!
I also didn't expect you to be such a fucking hack that you would squander all this potential you had in your show but I'm not going to run to the fucking academy and demand medals for that little subversion.