There are a lot of components to an operating system. It's not just the technology components, it's the product components and the business components. E.g., Does it have an API? Does it have an SDK? Does it have a user interface? Does it have an init system, a chron, a storage system, service discovery? Does it have an ecosystem of third party developers? I posit that the OS Checklist is fairly long and that no of the other systems you mention have the complete OS package.
If you were to look at SmartOS and Smart Data Center, you'd realize that it does have ALL of those components. The place I feel SDC and SmartOS fall short (of DCOS) is in application deployment/orchestration which I think is huge for devs who've had to manage VMs in the cloud.
Another win for DCOS is that it can run anywhere while SmartOS only runs on baremetal. SmartOS does come with some nice goodies like the Manta object storage platform and Manatee, a Postgres replication and failover platform. Application orchestration would make it a contender IMHO.
I posit that the OS Checklist is fairly long and that no of the other systems you mention have the complete OS package.
They do.
E.g. SmartOS is a UNIX. It'd be pretty odd if it didn't have an init system. Or storage. Or cron. Or POSIX. Or whatever else you'd like to add to the list that UNIX systems usually have...
That's just like your definition, man. Not everybody is that anal retentive about their definition of 'operating system'. (I doubt Tannenbaum would be in favor of yours, for instance).