I feel like medic is really strange for me in terms of enjoyability. It's unique in that experiences get exponentially more fun with medic the higher level you play, regardless of your *actual* skill level due to the innate dependability of medic on the rest of the team (keep in mind this comes at a detriment to your team's performance if you are not a high level medic so firsthand can't recommend the experience to people who like their friends). With DM classes because of the innate fun of "shoot man and die" and the relatively large change in mechanical complexity, its easy to have fun even if you're not playing well but getting kills or winning fights.
I think this is kinda why ultiduo just seems to be the *ultimate* medic fun mode; you're in a position as a healer where your damage and mechanical skill has much more impact and value, especially if you're not missing. Ulti fills in the mechanical gaps and exciting plays you would never even hint at thinking about going for in a 6v6 environment.