You left out a detail - the movie was terrible even by superhero movie standards.

Endless meaningless chat. Set pieces with no rationale behind them at all. Multiple characters with no actual purpose in the plot. Multiple gross plot holes, and as you point out, a plot inconsistent with the previous films.

I blame the writer(s)(*) for all of it. Yes, the actors are plastic when they aren't in a punchout, but that's what you expect in a superhero movie. But boredom? No. We watch these movies to be diverted.

Here's a real headline: Black Widow Writer Reveals Why It Only Took 11 Days To Write the Movie. This is my unsurprised face.

(* - one script writer, but two others credited for "Story".)