The DLC so far can be a mixed bag for many. The revealed characters are all 3rd party, but 2 of them have been prominent on Nintendo consoles in the past and 1 used to be 1st party. DQ, while not beloved in the West, is very much wanted by Japan so its inclusion makes sense for DLC. And I mean who honestly saw Joker or Banjo coming? I've not followed any leaks past the game's launch, but Joker and Banjo I never saw coming (heh). Persona (well at least 3-5) never saw any games for Nintendo except for Q and somehow Nintendo wanted to add Joker for whatever reason (there's also that Persona 5 Musou but that was announced after Joker's reveal trailer). For Banjo, I honestly gave up hope since I thought getting the rights to him would be a nightmare, but apparently not and Nintendo snagged him easily.
I agree it'd be boring if the rest of the DLC were 3rd party, but if their gameplay is fun or their reveal is unexpected or a popular pick (Geno for me), I'd be content with it. I bought the season pass not knowing what was to come, but I'm happy with all of them surprisingly but I could understand if other people didn't feel the same. The other spots could be Nintendo reps, but they'd have to "matter" for me. I wasn't happy with Piranha Plant, and I'd be darned if we get another FE character but after Banjo I don't really care who Nintendo adds.