Cosmetics are purely for the enjoyment of the one who applies them.
Because of the distances, speeds, and overall nature of the game, you never really notice cosmetics unless it’s something extreme, like a hot-pink Ronin on your team.
There is an exception in that you see the one who killed you very briefly. Even then, decals are quite tiny.
Much of the game is shooting at distant pixels and targeting boxes with high velocity long range weapons, it’s generally very impersonal.
I think it’s interesting to think about what the game would be like if things were scaled such that combat generally happens up close in visual range, and that weapons have projectile speeds that would make that the norm.
It is what it is, and players are no doubt used to it. To make a change of this nature would be monumental.