Think about that for a moment. Meteor isn't just a web framework, it's an entire platform providing code compilation and optimization. Otherwise, how would it be able to support ES2015 across both client and server?
As the Meteor folks said in the announcement:
And as a platform, Meteor has improved some internal performance factors as well in version 1.2. For example, the distributed data protocol (DDP) used by Meteor to send data (e.g., an Episode document) down to the browser now uses compression to reduce on-the-wire bandwidth. And on the server, Meteor has improved MongoDB oplog tailing logic to reduce the overhead of notifying clients of large numbers of writes.