I suspect there are few capabilities compose possesses that quadlets lack. Certainly, there are many capabilities that quadlets possess that compose lacks because you're really making systemd services, which exposes a host of possibilities.
Services are conceptually similar to pods in podman. Volumes and mounts are the same. Secrets or mounts can do configs, and I think podman handles secrets much better than docker. I searched for and found examples for getting traefik to work using quadlets. There are a few networking wrinkles that require a bit of learning, but you can mostly stick to the old paradigm of creating and attaching networks if that's your preference, and quadlets can handle all of that.
Quadlets use ini syntax (like systemd unit files) instead of YAML, and there is currently a lack of tooling for text highlighting. As you alluded, quadlets require one file per systemd service, which means you can't combine conceptually similar containers, networks, volumes, and other entities in a single file. However, podman searches through the quadlet directories recursively, which means you can store related services together in a directory or even nest them. This was a big adjustment, but I think I've come to prefer organizing my containers using the file system rather than with YAML.
Services are conceptually similar to pods in podman. Volumes and mounts are the same. Secrets or mounts can do configs, and I think podman handles secrets much better than docker. I searched for and found examples for getting traefik to work using quadlets. There are a few networking wrinkles that require a bit of learning, but you can mostly stick to the old paradigm of creating and attaching networks if that's your preference, and quadlets can handle all of that.
Quadlets use ini syntax (like systemd unit files) instead of YAML, and there is currently a lack of tooling for text highlighting. As you alluded, quadlets require one file per systemd service, which means you can't combine conceptually similar containers, networks, volumes, and other entities in a single file. However, podman searches through the quadlet directories recursively, which means you can store related services together in a directory or even nest them. This was a big adjustment, but I think I've come to prefer organizing my containers using the file system rather than with YAML.