"Nastiness, or at least blandness, seems to be an essential ingredient of the casserole."
That's because we grew up in the post WW II era of convenience food casseroles based on canned soups, canned vegetables, and salt. LOTS of salt.
I've never had a casserole made the "traditional way (canned crap)" that's not millions of times better being made from scratch by making your own sauce, using fresh vegetables, etc.
"Mac & Cheese - no thank you"
I've always suspected, but now I know. You're a *expletive deleted*ing Communist!
"Cottage pie, never heard of it."
Essentially it's the same thing as Shepherd's pie, only traditional Shep pie uses lamb, and cottage pie uses beef or even turkey.
Obviously a lot of the casseroles in that list from Wikipedia are from foreign countries/cultures -- France, China, Nordic countries, etc. I've heard of a lot of them but others, no.
And how could I ever forget Mousakka? It's one of my all time favorite dishes. There's a Greek diner near me that has incredible Mousakka.