Just a quick note that .babelrc wasn’t supported (and was ignored*) before Meteor 1.3.3 (currently at beta.2).
Had you used a later version of Meteor, your “high-tech” fix was almost right, just that you have an existing .babelrc (from mantra?) which would break Meteor. You actually don’t want the es2015 preset, since the auto-included meteor preset already covers this in the way needed for Meteor, and likewise, react is unecessary. Lastly, babel-root-slash-import will break Meteor and should be removed.
Note, transform-class-properties is also included in the stage-1 preset; but it’s definitely safer to enable these features as-needed.
* For the sake of correctness, there was an early release of Meteor 1.2 that worked with .babelrc by accident, that more often than not it would break Meteor (it would read a .babelrc from outside your project dir too). It was disabled shortly after.