I don't see how this is anything like compose. With quadlets you have to create a file for each container and deal with creating volumes and so on. Whereas with Docker it's one file, one command and you're done, you don't have to deal with anything else.
They're both declarative manifests describing how to run one or more images on your system. You use .container for a single container, .kube for all-in-one pods, .network for networks, and .volume for volumes. It has all the stuff it's just broken down in a more (imho) sysadmin friendly way where all the pieces are independent and can be independently deployed.
How's that better? How many files do you need to replace a complex compose project, 10? And you still have to deal with SystemD?