Of course, it's not all about data. The reason we actually change things is because of how they feel. One of the factors that contributes to how something feels to play against is how long it's been around. For example, even if best deck X felt alright to be the best for a week, players probably won't feel like that if best deck X is still there 2 months later. That's where data comes in. We've been watching gameplay trends in data for 15 sets now and have a pretty good idea what a meta looks like when it's about to see a shift and what a meta looks like when it's completely stabilized. The part where data doesn't help is when we have decks that cast Shudderwock 15 times or have an indestructible Lifestealing weapon. Those changes are based around feel and are what we generally come to places like reddit looking for.
In terms of communication, we first have to get aligned internally. This subreddit finds out what we've decided to do when we get a patch date in place, the official messaging has been written, and it's been translated into all languages. This process usually takes a week or a week + a couple days. This is all to say, once we decide to do a patch, you will all know within about 7 days of the moment we decide.