The quesion appeared many times in podcast and weekly AMA on instagram. As far as I remember the answer will be … it depends 
I am a simple man but my take is:
The main driver is total volume (example of a client of his who cut daily commute to work during pandemic, that has lead to low performance). I follow couple of his athletes (world level) and their z2 rides are sometimes extremely low wattage, but always quite long. Time pushing the pedals matters. Is single 4h ride better than 2x2h rides? Probably a little bit as long as 4h ride is not messing your life and you can do this consitently. In this case 2x2h rides will also be good as long as you push the pedals.
Then of course is the aspect of progressive overload as your body adapts to stimulus. So chosen workouts should follow this rule. But it’s impossible to push every ride to the limits as we have recovery side. So choose key workouts and progress through them (for example threshold workouts or key, long ride) and supplement rest of the week with volume that you can recover from.
No single ride can improve your fitness but consistency can. So bevare of “training camp effect” where people log big hours for 1-2 weeks but stimuli is so big that your body cannot cope, you get infections and waste 4 weeks for recovery. So build volume gradually (progressive overload) and pay a lot of attention for recovery.