There is no law that forbids galaxies to have their own speed. Imagine two idle cars on a rubber band. Begin stretching the rubber band and those cars begin moving away from each other. However if you start one car and drive toward another one you can overcome the stretching of the band and approach the other car.
It is actually known that galaxies have their own speed within the Universe and they can collide.
I would say the only evidence that is mounting is that we still do not understand the makeup of the Universe very well.
Did anyone claim that we understand the makeup of the Universe very well, just well, or passably good? As far as I know, very little is known about the Universe. The criteria of declaring your knowledge to be of the "very well" grade is when you can make your own little Universes, even if they are not perfect.
That would imply that a galaxy, for instance, can move faster than the speed of the expansion of the Universe. Would that not violate a few laws?
Did anyone claim that we understand the makeup of the Universe very well, just well, or passably good?
Well, yes. Every day scientists proclaim some new discovery or theory that they assure is is the absolute truth.
As far as I know, very little is known about the Universe.
Then you know far more than most people.
The criteria of declaring your knowledge to be of the "very well" grade is when you can make your own little Universes, even if they are not perfect.
It's all in our heads.