I agree with the Maffetone suggestion. If you make significant gains just doing Z2, that is a sign that you (like most of us, whether or not we want to accept it) still have a lot of room to improve our aerobic system / aerobic capacity.
If you could do 12 hours of Maffetone aerobic base trainng per week for 3 months or so, I think you would then be able to add intensity back to the plan in a much more sustainable and effective way.
6x 2 hours MAF rides per week, or 4x2 hour plus 1x 4 hour, would be tremendously effective.
I also agree with the intervals.icu recommendation. I don’t think there is a better cycling data analysis tool / data set anywhere.
These are the categories in intervals that you could compare your own data to
Consider having a read of this thread too Building and Measuring aerobic fitness