When I say tone and aesthetics, I'm talking about as movies as wildly different as once upon a time getting Spider-Man 2 and Batman Begins in back-to-back years, or even recently the difference between something like Deadpool and Logan, which is why I am one of the more vocally open-minded folks around here about "Fox-Men" in spite of, sigh, Kinberg's misfires.
When it comes to the MCU movies, what ties them together is far closer than what ties them apart. You can agree they all have a visual similarity, but narratively and tonally let's look at some of the others you listed. Guardians is one of if not my overall favorite MCU properties (shame they killed the golden goose), because there was so much of James Gunn's personality in it. That also is why he will be the first director they struggle to replace. Even so though, the first Guardians movie follows the same formula template of all the MCU movies in Phase 2, which post-Avengers is a bunch of disparate superpowered beings forming basically a band to fight a giant CGI threat to the world and/or universe at the end. The Guardians coming together to fight Ronan, Cap's team-up of Falcon, Widow, Fury, and Hill in TWS, Thor, Loki, Jane, and sigh, Jane's sidekicks in TDW, etc.
And tonally, they each use self-effacing humor as a defense mechanism, which is fine, but when they all do it they all tonally to varying degrees undercut their tension or differences, ironing out into an overall prepackaged feeling of similar safeness. So yes, TWS and CW play a little rougher than the other MCU movies, the same way Ant-Man plays a little softer, but you can feel the films engineered to get closer to a "default" scenario. In TWS, that involves a giant CGI slugfest and needless Macguffins in the third act so Cap can save the world, plenty of tension-deflating humor, and an emphasis on HYDRA so as to backpedal on any sincere political or social commentary and so as to not rock the MCU boat. CW embraces this more with the humor and glee of seeing Spidey trade barbs with Cap and Ant-Man grow enormous, so I prefer it. It also has the characters though in the "war" of the Civil War constantly joking with each other to suggest this is more of a friendly skirmish than a "war." Even the end that goes bleak, has to backpedal with Cap sending Tony a cellphone and basically apologizing, and then Tony making jokes at Ross' expense.
There's always a need to keep it right down the middle. Black Panther has the same third act problems as most MCU movies and still tonally feels very similar to most MCU movies, although thematically it adds more meat than most MCU movies, which is why I think it's one of the best.
Still, overall, there is a sameness that after 10 years is tangibly familiar. You look at Phoenix's Joker and you go, that's different! That is what some of us want more of. Not in the sense that they have to go crazy character actor/serial killer on something. But shake us out of apathy and come at this genre from a different angle.
