In Seasons 1 and 2, Rick was a barely functional alcoholic who got through life by running from his problems and being smart enough to rationalise away any action he could take. The show was intentionally stupid and didn't bother to focus on serious issues, because the fans were there to see insane comedy and not family drama. Season 1 was so out there they devoted an episode to Roiland blatantly improvising random shows off the top of his head, and it was most fans' favourite episode! However, as has been pointed out somewhere else in this thread, I can't remember where, Harmon's a control freak who needs each plot to be rigidly structured. Season 2's Interdimensional Cable episode wasn't nearly as good as Season 1's, so for Season 3 they replace it with a clearly scripted clip show.
Season 1 opened with Rick, drunk off his ass, struggling to even explain that he wanted to take Morty to the car. This was supposed to set the tone for the entire series. Now granted, Rick didn't stutter through every single line of dialogue, but the link to the show's improvisational roots was always there, until Season 3. Can you think of a moment in Season 3 where anyone was clearly floundering for what they wanted to say, or switched to a different word mid-sentence? There might be one, but I can't think of it. No, instead we got Rick talking to a therapist about how he's too smart to go to therapy and then looking all grumpy about it. Harmon probably thought that was really relatable.