For those who find it hard to do zone 2. It will be hard initially, coz you are not metabolic flexible yet. That's where zone2 training comes in. I like to add, don't refuel during easy run, you suppose to teach your body to use stored energy. That's why some runner s during rest days, they go for easy run, just to base built and get your body adapt to fat burning. Even on recovery days, they will do recovery run. The more frequent you do, the more your body become metabolic flexible and become efficient at fat burning.
ALso my own belief, there will be muscle and skeletal adaptation, since the intensity at lower than 85% of threshold are know to cause many adaptation in our body, and our easy runs are at that zone. I never had PF issues, or do I need braces for knee since the day I started running.
Also to note, LSD is not easy days even though it's in mostly zone 2.