I’m going to say that the main point, according to the article is that Rails+Backbone/etc is “tough” to set up. The argument presented about the designer having trouble with rails was a little silly. Because a designer isn’t going to have a learning curve for every project. It’s a one-time investment. Also, there is a time-investment for a designer to learn handlebars/etc in Meteor.
Also, Meteor seems to lock you into MongoDB, Node, etc. Which might be fine in some situations, but that isn’t always the right tool for the job. While Rails is opinionated, it’s not rigid. Meteor seems both opinionated AND rigid, which means in some cases you’ll be smashing a square peg into a round whole.
The Meteor “argument” reminds me of the PhoneGap/HTML5 app fad for iOS. Sure they worked and were somewhat easier to build by non-Objective C developers, however the performance differences between Obj-C and PhoneGap apps are pretty significant. Significant to the point that I can spot a PhoneGap app most of the time. The horrible performance from early Facebook iOS attempts were partly because they weren’t writing native apps.
I’m not going to dismiss Meteor completely, because I haven’t used it, however from my initial look, it the arguments for it aren’t very compelling, despite the hyperbole of that Differential guy.