I personally found the back bulge to be more comfortable to hold as a kid, it gave my hands something more substantial to wrap around. Honestly never knew that the GBC screen was smaller than the GBP until you just mentioned it, and I owned both. Learn something new every day! And the magnifying lights and worm lights were a blessing, they didn't exist (as far as I know) for the GB Pocket and the contrast switch didn't let me play that in the dark at all, so the GBC took me from being completely unable to play at night to being able to play with a silly peripheral (GB Light didn't exist in america). And I was too addicted to Pokemon as a kid to skip the GBC, had to have that Gold/Silver!
But I guess I can see the downsides to the GBC, especially for older people who had to actually buy their own systems (I was still young enough that every game system was a gift, not purchased by myself).