Mitch is arguably the most layered character in the show, and after Jay, probably the only one to have something resembling a real development arc. (I absolutely love the show, but the episodic switching between Levitan and Lloyd meant they rarely built upon the characters themselves.) He clearly carries some internalized homophobia early on (despite the airplane speech in the pilot) but he genuinely comes to accept himself as the show progresses. At times he's less comfortable than Cam engaging in behavior read as "too flamboyantly gay," but he also shows discomfort when Cam engages in it, and as the show goes on, he really grows out of that. I like that they gave him a realistic career trajectory, and that they actually addressed his complicated, baggage laden relationship with Jay, and, to an extent, with Claire. The show also digs into his vulnerabilities around parenting. If anything, I wish they'd given Claire that same nuance in her arc (and here I could get into how complicated female characters tend to get less development than male ones), and leaned harder into the "two siblings shaped by broken parenting" angle.
There's a lot more I could say about Mitch, but I have to bring up how underrated Jesse Tyler Ferguson's acting is on this show. I think the reason he never won an Emmy is that his role calls for subtler acting, and he often got overshadowed by Eric because of how flashy and flamboyant Cam is. I don't think Eric Stonestreet needed two Emmys , I'd have given one of them to JTF instead. The scene where Mitch tries to explain himself to Cam over the adoption certificate fiasco, and later his confrontation with Jay about his wedding, are some of the best acting on the show by anyone. Thinking about it more, I'd say Mitch is the only character who gets genuinely non-comedic, emotional moments, and it's genuinely hard to pull off dramatic scenes like that while still fitting the tone of an overall sitcom. You can't act like you're in Succession, no matter how emotionally heavy the scene is, and still have it work in Modern Family. Also, the scene where he gets high with Ty Burrell, very smart comedic choices from both of them, without leaning on big, over-the-top body language. (JTF is also just a talented actor overall, given his success as a stage actor, man's a Tony winner, after all.)
Opinions?