It seems to me that if you’ve a really large and complex client with a lot of things changing, many dependencies and multiple people collaborating on the code base, then I think it’s useful to be very explicit, transparent and develop a centralized and global source of truth on how each action changes the entire state of the client app.
For medium and smaller size apps, where one or two developers working on the front-end code and state changes are not that complex to grasp and maintain in the developers memory, then something like Redux might be an overkill. Furthermore Meteor does have mini-mongo and reactive data sources but it leaves it up to the developer to decide where and how this data will change. If the app grows in size and the developer continues modifying global reactive session variables all over the code, then you might end up with unexpected states, bugs that are hard to trace, and unmaintainable code.
But yeah I don’t like it when people blindly follow the latest trend and adopt the next shiny toy out there without careful evaluation of what does it really provide and whether it’s the right tool for the job in hand.