Avengers movies feature other Superheroes which had solo movies long time before Spidey:
Before 'Civil War':
Iron Man Captain America Ant-Man
Spider-Man's role in Avengers 3 and Avengers 4 was glorified cameo. Maybe he had more relevance on #3, but not that much.
Batman’s role in Joker was non-existent. Bruce Wayne’s role in Joker was glorified cameo.
It doesn't matter. The movie features NO superheroes. The movie focuses on the archenemy of Batman. It's a Bat-movie. Thomas Wayne is one of the characters. Bruce Wayne is on it, as well as his origin.
I wouldn’t say Joker is part of the Batman franchise, despite being a DC property with characters from that brand.
Catwoman (The Catwoman from the Burton movies appear on a picture) Suicide Squad (Batman appears) Joker (there's Bruce Wayne and the movie is about THE archenemy of Batman) Birds of Prey
They are all part of the Batman franchise.
Even Justice League is part of it. Batman is the primary lead character, Superman is the secondary character - Wonder Woman, Aquaman, Flash and Cyborg had no solo movies at that point.
I mean that’s your opinion. If you want to include all of them, more power to you. I might agree with JL to some extent since he plays a far more centric role in that than in Joker or SS, but that’d be like saying that Avengers is an Iron Man movie.