The statement about every opiate hits pretty much the same receptors is false. Some hit only one, some hit 3. Some are pure agonists and some are synthetic.
The route of administration matters with some. The dose matters significantly, everyone is different. The bioavailability affects some.
That is why there is a list of many different types of opiate analgesics.

Methadone works very well for me. It acts on 3 opiate receptors if I'm not mistaken. I also take norco which only works on one. But my doc still finds it necessary to take both. Methadone works for nerve pain in my case.

Usually doctors implant IT pumps and get patients off all oral meds. Some just lower orals. You can have other medications in your pump and the dose adjusted if you and your doctor agree on it.