Sean,
A couple of issues with mixing 80/20 zones and Stryd zones.
First, Stryd does not quantify what “critical power” is. See https://support.stryd.com/hc/en-us/articles/360039261314-Critical-Power
They define it as “the threshold at which the dominant type of fatigue your body experiences changes.” That’s not helpful in comparing intensity methods. I need some sort of Rosetta stone if I want to compare Stryd zones to 80/20 zones. Is it VT? LT? Anaerobic threshold? Aerobic threshold? CP30? CP20? Could be anything.
Second, even if I could quantify what “threshold” means to Stryd, we may not then agree on what “easy” or “hard” means, or even what “Zone 2” means. Their Zone 2 might include some or all of Zone X, which would be a disaster is you spent a lot of time in Stryd Zone 2.
In summary, no, they are not interchangeable at this time. My advice is to commit to one system or another for the best results. If you commit to Stryd’s intensity measures, you’ll do great. If you commit to 80/20, you’ll do great. If you try and combine them, there is some risk.
David