There's a good application of low power Zen chips coming up : https://www.tomshardware.com/news/re...apu,40399.html
Surface is high end, and they won't leave performance by the wayside if they can fit in the thermal/power envelope.
The Surface Laptop 3 is good for mobile processor mindshare. AMD replacing Intel in it makes AMD look like the new premium brand in mobile.
I still think Intel is better in mobile, but tbh I haven't personally used a Zen2 pc so I haven't seen it's low power speed and fluidity in low power uses like web, media, light office.
From a "needing to sell new products" standpoint going with Zen2 makes sense since Intel has been more of the same for a long time now.