It is if Grandma keeps downloading scams and installing them.

You mean there are no scams in the famous "we're protecting you from all those internet evil guys by charging you app subscriptions" app stores?

No, even then it still isn't. A device should not protect you from making bad decisions. It should be an aid in making good choices, not a nanny keeping you safe because you can't be trusted to do better.

So, turn off your firewall if you don't want to be protected.

Do modern OSes have services listening on external IPs without explicitly told to still?

I think to the parents point, everything should be wide open, all the features possible, and let him configure. By not listening, isn't that 'over-simplifying', let the user decide.

So because "Grandma" keeps doing stupid things with tech she doesn't understand, that now means the rest of us have to suffer for it?

Grandma has a tablet these days.

All the downvotes are really missing the point of Apple.

Simple exactly does mean less features. That is what you are buying into. Less features, easy to find, no 'ambiguity'.

If you want a ton of feature and flexibility, you go elsewhere.

But don't criticize Apple for being locked down, when that is exactly what they are selling.