In your day-to-day dealings on a ward, I would completely agree with you that the raw sciences aren't going to be something you're drawing from very heavily. And it's true that you'll receive the science in some form during medical school classes. However, the medical school material is largely applied science (as it should be) and there's little opportunity to explore the pure science further.
If medicine is only about observing symptoms and matching them to a pre-determined checklist of possible diagnoses and the appropriate treatments, then the science is completely unnecessary. In that case, doctors are also overrated and might as well just be technicians. I like to think that doctors are as highly regarded as they are not because they have a checklist memorized instead of being printed, but because they understand the disease process from top to bottom and have an understanding of how treatments can affect it. That also puts physicians in a position to advance the field of medicine as new technologies and treatments become available.
I liked some of the humanities courses that I took (particularly psychology), and felt that many of my undergraduate science courses were pretty poorly taught. This may reflect a current failure of the education system (or maybe it just didn't do it for me): it wasn't until graduate school that I felt I was really understanding and "living" the science, instead of largely memorizing it in a passive manner.
I can't really comment on the critical thinking that humanities courses develop, because I didn't feel that I developed anything in them. (But to be fair, my undergraduate science courses did a poor job of that, too, and it wasn't until graduate school that I really gained something.) I can't say for sure whether that was unique to me, or whether it was my classes. It's possible that I was approaching my classes too passively at that point. I know that many of my peers did similarly - it's a problem when people view science as something to just memorize your way through, rather than something to learn and link to real-world applications.
It's true that anyone is capable of contributing to the field of medicine, and I don't mean to disparage anyone who didn't study a science before medical school. It's also not as if someone finished with medical school can't or won't gain a deeper understanding of science as they go.
But why, after saying that medicine involves more than hard science, did you mention "communicating and working well around people"? I've heard before that one of the motivations to get non-science majors into medical school is to get people with better communication skills and better people skills. I don't know if that was your intention or if you share that belief, but that viewpoint bugs me. I've run across my fair share of awkward, empathy-lacking people who didn't study science, and I've met plenty of science people who were perfectly sociable. The stereotype that "science nerds" don't know how to work with others in difficult situations is trash.
If a bio major is a waste of time, then any undergraduate major is a waste of time. I'm kind of surprised to hear you say that, when you had previously said that any major can contribute to medicine by "bringing new ideas to the table" (which I agree with). By any chance, did you have a bad experience with a plant biology class?
In all seriousness, it's true that you'll learn most of the basics that you need to treat patients in medical school. But what separates physicians from the other workers in the healthcare field? As I wrote above, I like to think that it has to do with the fact that doctors have a deeper understanding of that which is unseen in the disease and treatment processes. Otherwise, we're just technicians who claim superiority because our program is four years instead of three.
I've seen doctors who were basically technicians, having a superficial understanding of the disease process, and I've seen doctors who encompassed the ideals that I'm describing. They both do valuable work, but the former seemed as if they could be replaced with experienced nurses with little to no consequence. As someone on the physician track, I'm interested in physicians remaining differentiated and valuable as a position not because legislation limits the other positions from doing certain things, but because physicians really do know and understand more.