Blaming a whole company's delivery problems on a local courier is a little too simplistic.
The problem with delivery companies is the service is dependent on many factors.
Yes, the end of line is a local courier (possibly self-employed) but a local courier works in a very small area - usually a single postcode, and this can mean one person can have a wonderful service and 5 miles down the road a not so diligent courier provides a poor service.
Problems relating to couriers usually involve delays where people live in outlying areas and couriers keep parcels back until there are several in that area - and the reason they are forced to do that is because of very poor pay. It's not worth travelling a 10 mile round trip if you're only going to be paid 85p for your trouble. This would probably only result in a delay of 2-3 days.
I recall Dazzler's problem with her bucking bronco. That didn't arrive for weeks - and I don't for one moment think that was down to the courier. No courier with a brain would keep a large item like that stuck in their garage for weeks on end - most couriers want to shift parcels asap.
Ideal World ship some things out from their warehouses and some are obviously shipped direct from the supplier - but they don't make it clear when this is happening, so as usual the poor courier gets the blame.
Before the courier is given the parcel, there are any number of things that could cause a delay (apart from IW that is) - labels being ripped off; item having to be returned for relabelling...parcel getting mis-sorted and ending up being sent to the wrong depot/subdepot; parcel being nicked, never to be seen again. NONE of these things can be attributed to a courier, it's the fault of the Delivery Company.
Because of the way delivery companies like HDNL and Hermes work, you inevitably cannot bundle their part in the logistics service with that of the courier. Each courier, whether employed or self-employed has no control over what happens to parcels in between IW and receipt by courier. Similarly, couriers (whether employed or self-employed) to a large degree are in control of when they choose to deliver and if they are particularly busy one day, or quiet in an area another day, parcels will be carried over.
I don't think one factor can be blamed: you really are in the lap of the Gods when placing an order with any online company and getting to know your local courier can help - particularly if you are privy to their phone number (something you will get with Hermes couriers, but not HDNL/DHL etc).