Except we:
1) optimized our database operations
2) relegated cpu-bound work to micro-services that could process work from a queue at their own pace
3) Leveraged the ecosystem to writer smarter and more concise code
Know your enemy and know yourself and you need not fear the result of a thousand battles (Sun Tzu). Meteor is an amazingly productive ecosystem for writing real-time applications. No it will not solve every problem you throw at it.
Just to be clear I'm not hating on Horizon. I definitely will try it in the future.