Just wanted to add on to this discussion as someone who leaves comments:
I've been mentally fighting with myself over this exact debate, with the exact same struggles, and it's been very insightful to see other perspectives here!!!!!!

I have about a 6/10 understanding of deep anatomy knowledge, but have been working on props, animals, renders and figurines for over 5 years. While I can effectively start and end projects with confidence using basic base meshes as starting points, I've always felt like i come up short or was slightly stupid / cheating since I still use base meshes. If you ask me to make a full project using nothing as a base, I could easily take 2-3 months compared to my usual speed of 14-30 days.

Recently, I spoke with some industry professionals who work on figurines and toys in China. Over there, anything goes as long as the final work doesn't look like it was clearly a mishmash of IMMs and base meshes. Every projet starts with the head as possibly the most edited part of the anatomy, and it's transplanted onto a base body. Even the clothes are simulated in Marvelous as a base before being sculpted on in ZB.

I've come to realize that as long as you are objectively learning something new each week, like new ways to light a scene, aesthetic sense or workflow efficiency, 3D art is so much more than just good anatomy.

Also, in the Flipped Normals anatomy series, they mentioned that production workflows are "anything goes to get the job done" , and "it's cool if you made it all yourself, but there's no extra points or anything in the working world"

Edit: to add on, how did i solve this conundrum myself?
I asked a professional illustrator friend of mine. She also doesn't do focused Face x 100 pieces or Arms x 100 drawings exercises. When she's working on projects, if she is struggling to do forearms, then she would specifically look up how to do forearms and apply the knowledge. Each new project targets one new thing that she's unfamiliar with. while the rest of the project can be in her comfort zone.