Law and Order episode was a great one, and you're right, the best Harmon episodes were the ones where the gimmick didn't interfere with, and even enhanced, telling a meaningful story about the characters. But I think 'we got to see different facets of the characters' is a rose-tinted way of saying that the characters have been written extremely broadly and at times inconsistently. Pierce in particular went through a lot of incarnations, and it never felt to me like he was deliberately being evolved so much as he was modified to serve the story. When they needed a bully or an antagonist within the group, he got meaner. When they needed someone in the group to be isolated, they made him into a more pitiable figure. When they didn't have need of either of those modes, he was just a delivery tool for weak punchlines.

I think being true to the characters is only true in a roughly fanfictional sense, where these characters had certain core elements that had to stay true no matter which AU they were placed in, for it to feel canon-compliant. I don't think there was actually much consistency in the character motion over the course of seasons because the jumping in styles made it impossible for that to be meaningful. Did the character discoveries of the paintball episode really translate over to the Law and Order episode? Only in a very loose way.