I've been doing a bunch of figure-drawing zooms recently, and while I have been increasingly happy with my ability to draw and shade a proportional body in a fixed time span, I have been increasingly frustrated with faces. So this evening I decided to practice face drawing. 
It turns out I can do this after all. I can't find a link to the reference photo, and it's not my photographic work, so I am not including that here, but you can trust me that this is recognizably the same person as in the photo I was drawing from. It's not perfect - there is always more work to do. But it's WAY better than I could have done even six months ago, and I am very pleased with how it came out.
So I went to my old sketch books and compared a 15 minute drawing from 11/29/2020 to one I did this morning, and it turns out that (even though the faces in today's sketches were still pretty cartoony), my figures are MUCH better after two years of additional practice, so I am feeling better about this whole thing.
I think these are the factors that have been limiting my success drawing faces during figure zooms:
- Tonight's face drawing, above, took me a couple hours - It is not fair for me to ask myself to do this and ALSO draw a proportional and well-shaded body in 15 or 20 minutes.
- Tonight's face drawing takes up most of a page in my sketch book, whereas faces in a figure drawing sketch are much smaller, so it's hard to get the details in there.
- I am also, in these figure zooms, comparing my sketches with sketches by artists who are much more experienced, or, in a couple of cases, just much more natively talented: Sometimes one person learns certain skills faster and more easily than another, and that's natural and good.
I have been lucky in my life that most things come pretty easily to me - but I am almost never able to compete with people who are truly talented in a particular skill. I was decent at blacksmithing, knitting and crochet, an excellent writer. I am a terrible bowler, which my athletic mom does not find embarrassing at all, god bless her, but I can reliably get the ball to the end of the lane and hit one or two pins, and it's not like I spend a lot of time practicing to be a good bowler.
In most crafts, my work gets noticed, people acknowledge my competence, and the ribbon goes to someone better, and that's fine because this is not a competition (despite my ribbon metaphor). I am doing this for fun, and so that I can eventually draw some graphic stories I have in mind. It's ok for professional artists to draw beautiful faces and perfectly realistic bodies in the time it takes me to draw my totally reasonable sketches.
It's been a good day for introspection and self-examination.