This is an interesting subject! I have a Levo SL and since I started riding it I have lost that ‘I have to ride tonight or I’ll lose fitness so wont enjoy riding as much next time’ attitude. Basically, I’ve lost the anxiety I used to have about losing fitness as I know I dont actually need to be as fit as I used to think I did to enjoy riding my bike.
Make no mistake though, you can still retain fitness if you ride Ebikes, maybe not as much as with regular bikes but you can still work hard if you want to, you just go faster.