It's just advice, like I said. Not everything is spelled out.
And I didn't say that not taking upper div bio is fatal, just that it's not advantageous to NOT take upper div bio. No digs at the OP
We are in agreement then?
I think so, however if OP has a high sGPA so far through the typical pre-reqs and ends up taking a bunch of upper level bios, in addition to classes that are actually required for their degree (and perhaps gets a B or C in one/some of the difficult upper level bio courses), I think it will be more detrimental to their application than if they just took what they needed to take, along with say Biochem and A&P.
I took a ton of upper level biology courses because I was a biology major and enjoyed them, even the ones I didn't get As in. I just think there's a proper balance for a non-science major to take upper level Bio courses. Some of them can be quite difficult, along with what I'm sure will already be difficult, major-specific upper level's OP is actually required to take. OP shouldn't take on more risk than what is needed to gain a medical school acceptance. I think it's important for OP to take
some classes beyond the bare minimum pre-reqs, but definitely not important to take Molecular, Developmental, Immunology, etc., and things of the like. They
might offer
some help when OP does go through MS1's pre-clinical sciences, but assuming OP has a lot of other upper-levels that are actually required for their degree, it's just not worth it, especially if it delays graduation.
edit: I will note that this advice does largely stem on OP's actual, current sGPA. If it's closer to 4.0, the need for additional display of upper level science comprehension decreases. If OP got a few Bs in the prereqs that brings their sGPA down closer to 3.5, then the need for the additional display of upper level science comprehension increases. There's definitely a balance to be struck. Personally if I was in OP's position and I was sitting somewhere around a 3.7 and I did the math and saw As in Biochem and an A&P would get it north of a 3.8, I'd focus on that and planning adequate time for MCAT prep, without worrying about racking on many more upper level bio classes. A 3.8+ sGPA comprised of ~40 hours at that point with a great MCAT will garner a lot of attention from medical schools.