My only experience with numbing is the dental anesthetic they use in your mouth, which I don't recall producing much sensations but it does noticeably take sensation away.
Those aren't narcotics (most likely). It was probably Novocaine or Lidocaine. Those drugs end in -caine because they're all part of the same family as cocaine, which is not actually a narcotic (but does have euphoric effects at sufficient dosing levels!).
Topical use of any of those drugs, however, will likely not produce euphoria.
One could easily resolve the question of whether opioids cause euphoria by doing a double-blind clinical study. I would love to do that study, in fact.
Or maybe you're right: they just take away pain. But it turns out a lot of us have existential pain so it works all the time.
[1] http://www.rxlist.com/oxycontin-drug/side-effects-interactio...
For the benzodiazepine class of drugs it's a little less clear cut - people who take them recreationally may well be alleviating stress or anxiety and finding that pleasurable. Opiates.... nah.
I thought that I felt euphoria the first time I took codeine (but I honestly wasn't sure). I have taken codeine since and was never able to replicate that euphoria.
IME with opioids, there will be times when they feel good (or seem to), but those good feelings are frustratingly hard to replicate. I've taken a skeptical look back at all my use and concluded that the drugs simply don't have the power to cause euphoria all by themselves. They can be sort of like a social lubricant, and they can be reliably good when I feel like complete shit. But I never figured out a way to conjure euphoria on command using just opioids.
I'll throw it right back at you - your own personal experiences are worth about as much as mine when it comes to medical evidence, not a lot.
[1] http://www.rxlist.com/oxycontin-drug/side-effects-interactio...