There's absolutely know way they're finding out just now, because they made 1-2 Switch. In their own designing and testing they have definitely had people standing between the Switch and the joycon before. It's completely absurd to think this wouldn't have been tested.
I mean this is a statistic about the console like any other, something they measure in different situations and use cases. It's like if we discovered that the controllers have a 10 minute battery life and saying that they must've designed them plugged in the whole time and never tested the life, and are just finding about it now.
What I'm saying is, they know this is an issue and they also have a fix, because there is no way they could've made and sold 1-2 Switch and ARMS without a fix already planned.