Okay, first off, I do not write, 2nd, I barely passed high school english. Now this line:

The major culprit, when it comes to telling, is overwriting.

may not always be true. "Overwriting" indicates longer, more words. On that point about "Telling", I think I would disagree. Showing can take a very short boring line and make half a page of reading when you switch to showing a scene. And I do not mean all the miniscule little bits of iota like the grass was green and needed mowing it was so overgrown.

Take your cancer examples:

Jim was sad she had cancer.

vs.

"Hey, you seem down. How's the chemo going?" Jim asked.

"Rough," she responded.

and then:

I couldn't figure out why Jim was so sad. I knew he was going through chemo, but he looked even rougher after his last treatment.

Combining the two solutions to Jim was sad she had cancer.
.

"Hey, you seem down. How's the chemo going?" Jim asked.

Jen couldn't figure out why Jim was so sad. It's not like he was the one going through chemo, but he looked even rougher after his last visit to me."Rough," she responded, trying to sound just a little bit upbeat for Jim.

I don't know if I used a lot of adverbs or not, or if it is more visual than telling. Just seeing if I kind of got the gist of your post. Because i like longer books more than short books, and yeah at time I really do not like it when an Author or storyteller think their audience are imagineless lumps on a log.