Respectfully, I have to disagree. Fundamentally, you can correlate heart rate with power, but that is an average effect, and it will be wrong for a lot of people. For example, take the 220 - age rule for max heart rate.* That is an equation that predicts the average max HR given your age. That may be accurate on average, but for you as an individual, it may not be. You will have some people with relatively high HRs, and relatively low HRs. For example, by that formula, my max HR should be 180. But I know I saw 186 during my last ramp test, and I clearly survived that experience. Also, heart rate lags your power output, so if you go hard in a race, it takes some seconds for your heart rate to catch up. And heart rate can also be influenced by a lot of things, like rest and caffeine intake.
I don’t think Zwift should accept data from HR to power apps, but I can’t control that. I can say that these are not that accurate, and they may be even less accurate than the power curves on non-smart trainers.
*NB: 220 - age is not actually accurate on average. I’m just using it as an example because it’s a well known rule.