We've also seen instances where visible "clumping" in a galactic disc correspond to differences in the rotation curves, which dark matter can't really explain. But this is still a topic of much debate.
However, there's lots of good evidence for dark matter besides rotation curves of galaxies. For instance, models of galactic formation work a lot better with it than without it (without dark matter, as galaxies coalesce, they get hot and the pressure keeps the gas apart and makes star formation really hard).
We also see the Bullet Cluster, where two galaxies collided/passed through each other. The gas and dust has been slowed down from collisions, but the dark matter has passed right through. We know this from the gravitational lensing. The lensing happens around the mass of the galaxy, but with the bullet cluster, the lens is off to the side where there is no normal matter, because the dark matter kept going when the regular matter slowed down.
In other words, we have some really good evidence for dark matter, but there's a few things going on here and there we can't explain.
I remember reading/hearing somewhere that the bullet cluster actually fits MOND better than dark matter. I think it was a video by Sabine Hossenfelder but I can't find it right now and I'm not qualified to say whether it made sense or not.
Bullet cluster is inconsistent with LCDM on the grounds that given the apparent dark matter:matter ratio a collision between clusters of that size is something like unlikely to the tune of one in a trillion? IIRC universes. (Aka the collision should not have happened in the first place).
The thing about lensing is that we don't have a solution in (GR would need to be tweaked if MOND is true -- the math is much harder!!) so we can't really say what the lensing would look like in any given MOND-like theory yet. Seems weird to declare that MOND can't explain lensing. It's should be more qualified: "we don't think MOND can explain the lensing"
It's not clear that GR would need to be tweaked to match MOND. The GR solutions we currently use in LCDM are based on the FLRW metric, but that metric could just be the wrong fit for our universe.
I wasn't familiar with the Bullet Cluster[0], but as you described it made it very interesting. I'm no astronomer, but from all of the examples of gravitational lensing[1] I'm familiar with have a very distinct look that I'm just not seeing with the Bullet Cluster. Where is the lensing effect occurring that is leading to this theory?
Gravitational lensing doesn't have to be apparent to the eye as those extreme examples on the wiki page are. The second image on the bullet page shows matter in pink and measured lensing in blue.
I thought gravitomagnetism was extremely weak? Wouldn't normal magnetism and its interaction with environmental plasma (which IIRC is also neglected on the grounds of being a rounding error) be more significant?
However, there's lots of good evidence for dark matter besides rotation curves of galaxies. For instance, models of galactic formation work a lot better with it than without it (without dark matter, as galaxies coalesce, they get hot and the pressure keeps the gas apart and makes star formation really hard).
We also see the Bullet Cluster, where two galaxies collided/passed through each other. The gas and dust has been slowed down from collisions, but the dark matter has passed right through. We know this from the gravitational lensing. The lensing happens around the mass of the galaxy, but with the bullet cluster, the lens is off to the side where there is no normal matter, because the dark matter kept going when the regular matter slowed down.
In other words, we have some really good evidence for dark matter, but there's a few things going on here and there we can't explain.