A lot has been made about the change in tone that Thor saw in between the character's second and third film entries. While that change has clearly had a positive impact on the box office results, that may not be the only reason it was made. Many have made the comparison that Thor: Ragnarok resembled the Guardians of the Galaxy movies in many ways, and this comparison is apt for a number of reasons. The two franchises share a lot of elements, and based on the current rumors about where the Marvel Cinematic Universe will be going from here, there's a good chance that a lot of the MCU will look like a lot like Thor: Ragnarok. If the change in tone was made because all Marvel "cosmic" stories need to have a similar tone, then we'll be seeing a lot of that in the future.
The first Guardians of the Galaxy movie was a unique animal for many reasons. It was a lesser known comic book property and right out of the gate the film had a much lighter tone than the other parts of the MCU. The Marvel universe has always been a place where humor was welcome, but this was taken to an extreme in Guardians. You wouldn't describe another Marvel movie as a comedy, but that title wouldn't be out of place with that one.
The other thing that Guardians did that was different was take place in outer space. The vast majority of characters weren't human, and the storyline barely touched on events taking place where the rest of the MCU was located. This separation was part of what allowed the Guardians to be so different. However, as we stand here on the edge of Avengers: Infinity War that separation is about to vanish, so it's little surprise that Thor now looks so much like the Guardians.
Thor is, after all, not human. He's a god from another planet, and "alien" like most of the cast of Guardians of the Galaxy. He's probably got more in common with Rocket and Groot than he does Tony Stark. Making Thor feel more like the Guardians will likely make him work well as the bridge between the two worlds when everybody comes together in Infinity War. However, there might be even more to it than that.
While it's far from clear exactly what form Phase 4 of the Marvel Cinematic Universe will take, the current rumors are that it will be much more cosmic, dealing with more characters in space. The current belief is that Guardians of the Galaxy Vol. 3 will act as a sort of launchpad, creating new characters and storylines that will be the focus of things going forward. If this is true, then there are some conclusions we can draw. If Thor: Ragnarok and the Guardians of the Galaxy movies have told us anything about the cosmic part of the MCU, it's that it can be a silly place.
If there are more Thor movies, we can safely assume they'll follow the tone of Ragnarok, and that, combined with Guardians, pretty much defines deep space as a place where humor is strong within the MCU. While not every film in Phase 4 is likely to be so light, it's very likely that the ratio will be flipped in Phase 4, with the majority of the story being told among the lighthearted cosmic stories, with the occasional Earth-based, and somewhat more serious, hero story popping up every now and then.
The shift in tone in Thor: Ragnarok brings the movie in line with the Guardians of the Galaxy franchise, and the general feeling that this corner of the MCU is funnier than the rest. Since that's the corner we're likely to be focusing on after 2019, it's a tone we should start getting used to.
