Honestly this is pretty good “time in zone” for a hilly outdoor ride.
For z2 ride, it is better to do it by HR or even by RPE, as long as your perception is that you are doing it easy, it´s OK.
Thanks Feltz for reminding me I’m back below 4w/kg 
I think I’m running a 48/35 and 10-30 in the back.
just keep it chill and don’t burn matches, the basic idea behind aerobic endurance riding is to increase saddle time while reducing the recovery time. Adaptations to muscles only require minimal power - its driven by the number contractions - so more time pedaling is one goal. Similarly adaptations to the heart also happen. Both take years, not weeks or months.
The other way is to increase the number of contractions per unit of time.
pragmatically that didn’t move the needle for me over a 2 year horizon, versus the last 3 years, although we are talking about very long-term adaptations… Also “scales with” is a bit hand-wavy. Thats my n=1 and my read of the science.
Got a similar problem to OP - solved by getting a goat link (GoatLink – Wolf Tooth Components) with compact chain rings and a 11-46 cassette. Can stay in Z2 quite easily.