I hold my opinions on this because I went to a mid-level private school and had a 4.0 GPA without even trying (okay 3.9 something. point is the same). It was clearly challenging to some, and it was the pre-med curriculum... it just wasn't a school known for it's pre-med education. They did have teachers who also moonlit at the local CC. I didn't have them (adjuncts weren't allowed to teach pre-med cores), but people did and they felt the same way: challenging to some, very easy to most.
I transfered to a high-level public university where I shared most of the professors for my cores with two different Ivy League Universities (as best as I can tell there is only one region where that is possible to do easily, so I may be locating myself with this). At this institution it was SIGNIFICANTLY harder to get even B's. My GPA dropped dramatically and everyone found classes very challenging. My GPA wasn't fantastic, but it was decent enough by the end to not close too many doors. At this school we were told by admissions officers who would come that they realize we get lower GPAs and get our asses handed to us academically, and they look past the GPA when they see what school we went to. They said that, at least in the states bordering my alma mater, the medical schools are all aware of the grade trends and a decent score at that school is considered on par or better than a gpa a few decimal places better at a weaker school.
I can say that one interviewer told me the same thing right in my interview ("dont apologize for your GPA, we see this a lot from <my school> its a pretty normal score for applicants from there") Admittedly I got waitlisted and never came off the waitlist there, but it was comforting to hear it right in an interview that they realized a 4.0 at the private school of questionable quality doesnt equal up to a 3.3 at a school known for killing you with the toughest education they can.
are my experiences applicable to everyone? Not sure. But I'm willing to extrapolate out if you're willing to allow me.