Really short version: it’s very immature, lacks good library support for almost everything, and being optimised for rolling deployments comes with its own set of compromises that many don’t want to make. Not to mention it’s not very team-oriented, there’s not even reviews before deployment feature.
Deployment speed is a very low-priority metric to optimize for, IMO.
The biggest drawback is that it’s closed source, so companies won’t ever adopt it, and this skill will only be great if you wanted to develop something of your own solo or with a small team very quickly, and still if they gone out of the business (which is highly possible with a closed source tool having a very small team and not backed by a big name like Google or Microsoft etc), you’ll be on your own.
And the deployment is done only to the infrastructure they set up, I hated that thing with Meteor where the only easily scalable deployment option was the Galaxy, the infrastructure they set up. Otherwise Meteor was a great tool.