I looked into this a while back, and Service Fabric was a clear winner over k8s, and resource use was a fraction of k8s too.
But, I felt it needed to gain community traction before I could commit to using it - knowing my luck, I'd build something and Microsoft would abandon it because k8s...
Kind of a chicken and egg problem, which is a shame really.
I think it's more fair to say the suit different use cases (an MS person on HN explicitly said this last year), rather than competing.
What features do you believe it's missing?
You can build Service Fabric manifests with XML.