I think it might be somewhat true because a lot of people have the D+ option and know they can just wait the couple of months to see it. I think if the wait is 6 months or something you'd see something different.
Those other movies are massive sequels to massive originals. Marvel is just a different beast. I do think they're doing too much and need to scale back.
This is pretty much my thinking as well. It is certainly not universally true and it is awesome to see that certain movies can still do very well, but I do think streaming has hurt a lot of movies.
Streaming can make it easier for people to skip the theater and wait for the movie to stream and it creates a mountain of options that can make it hard for “middle class” movies to break through.
There are also big movies that never even make it to theaters, such as “Glass Onion” and “Killers of the Flower Moon” (with DiCaprio, De Niro, and Scorsese).