That's definitely not true, because I've had parcels delivered by the postmen and couriers all the time. However, as we live in a quite rural area, the postmen are usually going around in their wee vans, so it's probably easier to carry the parcels around.
Ditto for where I live, which is pretty rural. The postmen are generally easy-going and helpful, and they get to know when neighbors are friendly with each other and will leave parcels with them if nobody happens to be home. I'll often sign and accept a package for my neighbors when they're out, and vice versa. The same goes for the regular delivery drivers for the independent couriers.
However, as I discovered a couple of months ago, Royal Mail no longer allows postmen to collect any money due, so if you have an international package which has customs duty/VAT due on it, it will stay at the post office until the tax is paid. You now just get the card delivered, giving the option of going the the post office to pay the fees and collect, or paying the fees through their online system or by mail,
then they'll deliver it.
If we have a larger parcel, that invariably comes to us through some other service (like Parcel Force which is, I think, run by Royal Mail?).
Yes, Parcel Force was created as the separate division for larger packages when the Post Office's functions were divided up some years ago, so if you go to the Post Office and send a package using the "Standard Parcels" service, it will be delivered by Parcel Force.
Our regular Parcel Force guy here is very helpful, and will try to leave packages with neighbors if he can. Sometimes we'll put a note on our doors if we're expecting a package, have to go out, and know that a neighbor will be home all day.
I even had one time when I was passing through another village about a mile from here on my way home, saw the Parcel Force van heading the opposite way back toward town, and he flashed at me to stop as he'd just been here trying to deliver and none of my neighbors happened to be home.