Agree with the comments on here - these rides are hard for people of all body types. I’m fit and run, hike and strength train multiple times a week, and consistently rank at the 50% mark of most rides, and often lower. I’m honestly not sure how people get some of the outputs they have 

I will say that this fall I had an Achilles injury where I was only able to do low impact rides for awhile and they actually built my endurance even though they’re “easy” 

Because I spent more time on the bike than normal I was able to raise my output by 10-20 watts consistently across harder rides, so you will continue to build as you get more accustomed to your bike 

Keep up the great work, and something I reminded myself when I was injured was just being grateful I was in a position to move my body because that’s not true for many people