Let’s all be friends 
I think the “don’t worry too much about a few watts here and there”’message is clear. A few watts/ calories missed if at 55% not 60% aren’t going to move the needle or the adaptations.
I agree that the benefits of endurance work inside (no traffic lights and downhills or cars) make it worthwhile. Also it gives a chance to catch up on YouTube or watch sport which is time efficient too!
One other thought - has anyone seen research cited around the best % of FtP to perform z2 rides at? Ie is my original thinking of 60% being good and 70-75% verging on being too intense correct?
Thanks everyone.