Yes, everything is irrelevant in a grander scale.
But it isn't irrelevant to you, and you should be your primary concern. Not the grand scale of the universe, you. I mean, for example, you like eating right? Boom, that there is completely irrelevant to almost everything that will ever happen. But to you, that's awesome. And let's say a galaxy 16 billion light years from here (beyond where we could possibly see) sinks into a single super-massive black hole. To the universe, that is fucking huge. To you, utterly inconsequential. And you aren't the universe, you are you. And the universe isn't fond of the human race either. We could develop world peace, nuke ourselves into orbit, enter a golden age of science, and to the universe, that doesn't matter, but that doesn't mean it doesn't matter to us. So be concerned with the you, and the universe will concern itself with itself, and everyone will live out their lives, except the universe, which is non-sentient, non-sapient, and not alive. Your morals and ethics shouldn't be based off the universe, they should be focused on the narrow realm of human affairs.
Also, that's pessimism. Cynicism is seeing things as they are, not as they ought to be. Pessimism is just natural opposition to Optimists, who are numerous in number and constantly multiplying, requiring swift and decisive action against them.