I agree in principle with your first point, but I guess for me it's more a matter of degree. The earlier books (the first one especially) are quite cartoony and Roald Dahl-ish, and all of them have aspects of it. I'm not comparing it to Shakespeare, but to something like Cedric's death, which IMO had some gravity appropriate to the setting and situation.

I think you have a good point about a mother's love, it does seem to hearken back to Lily, and I wouldn't be surprised if JKR intended that.