Wouldn’t wind just affect how far you travel (or how fast you go) and not how much power you are putting out, just like a bike power meter?
No. The key here is at the end of the sentence: “at the same pace.” Running a 6:00 min/mi pace into a dead on 20 mph head wind is harder (requires more power to maintain) then running a 6:00 min/mi pace directly out of a 20 mph. If the Stryd only uses accelerometers on your torso to estimate power output then it is unlikely that it can account for certain environmental changes like wind. Mind you this is my presumption based on my knowledge of accelerometers and signal processing; I don’t know what the Stryd algorithms are actually doing.
Bike power meters work the same way: ride into a head wind at 20 mph, then turn around and coast along with the wind at 20 mph and the power outputs will be very different.
Exactly my point. On a bike, power to go a specific speed varies with wind direction. Same with this system. This is exactly what you want. It IGNORES wind, just like a bike power meter and measures only the power you are producing. It does not have to account for wind and should not. On a bike, you have speed and power. On this device you have pace and power. That is all you need. In other words, this system is estimating power by measuring acceleration. The estimate of power is dependent of wind, as it should be.
Using your example, run a 6:00 pace into a head wind VS tail wind and you will have to produce a higher acceleration into the wind, which presumably this device will measure, therefore more watts. Just like a bike pwoermeter. Wind does not matter for measurement purposes.