Is your stance is that UMs should be allowed to dominate all media because if other chapters had more of the spotlight it would somehow be equally bad?
Because that really doesn't make much sense.
The whole point of having loads of chapters is the diversity of it.
There's no good reason why werewolf viking space marines needed to exist or any other bizarre permutation of what a standard astartes force should be.
But it's the most popular faction and it makes sense to let people choose their flavor.
There's literally 1000 chapters and most media focuses on the 1.
1, which I might remind you, is no bigger than any other of the 999 chapters.