I agree with you that it probably is not easy to pick up, but I have to admit, there is significantly less to deal with. Meteor is the fullstack, and it even has sockets built into it. You definitely have to buy into one ecosystem, and that's convenient because you don't have to know a serverside ecosystem (e.g. Rails) and a frontend ecosystem (e.g. Angular, React, and Ember).
Sure, but my current ecosystem is npm. For browser-specific substitutes to node-specific code I simply use browserify. If I decide React is boring, I can switch to an entirely different front-end without changing anything else. For stuff that isn't on npm I have to work with bower or something else, but that (i.e. ecosystem-external dependencies) is a problem in any application, not specific to npm.
With Meteor, you're developing Meteor apps. Sure, you can put a different front-end in it or replace its server-side with an API compatible equivalent, but that's like saying you can use Django without its template system or ORM (if you don't know anything about Django: you can, but Django's built-ins provide a lot of synergy that you can only get from tight coupling).
