Meteor came out before async-await was a thing for Node. Meteor solved the callback hell with fibers. However fibers introduced concurrency bugs. A fiber has pre-emption points when doing IO. If some other code then changes some state then it can be dangerous because of data races.

A friend of mine got stuck on a bug where sometimes he got a different value than he expected and after a walkthrough I showed him what happened. So Meteor is not really friendly to beginners if you have the bad luck to provoke a data race.

This is the main weakness of Meteor. I was not surprised that MDG pivoted to Apollo.

My friend is still happy with Meteor, because I told him where to look for concurrency problems.