Testing is still a third-class citizen in Meteor for some reason. The official guide mentions testing, but in the four times I've tried to follow it over the course of a year, I could never get it to work properly.
On the flipside, using Elixir and Phoenix you know exactly what's going on and why, you have real control over your DB queries. You can benchmark properly. Your tests are 100% real and accurate, and run properly. It's much better. You sleep better at night that's for sure.
I say this as someone who has used Meteor for multiple projects and used to love it!