Being an everyman works only if you have flaws that the audience can relate to. Graham doesn't qualify for me. He's a bigger boyscout than Superman. That's part of the appeal of Graham. He's a stand up guy, he can do the impossible, but he's a bit too good to be true. He's not flawed at all. And that's not a criticism. It works for the character.
Other than sending maidens off to be sacrificed to the dragon, including his own daughter... Sure 'flawless'.
How did I know that would get brought up? I almost put a caveat in my post, but figured I ramble enough as it is. Yeah, that's a flawed moment for Graham, but the difference is that we never see it. We see Graham as the virile boyscout (that felt wrong to type) in KQ2 and then we see him as the rejuvenated virile boyscout (ok, that really felt wrong to type) in KQ3. We never actually see a beaten down, flawed Graham. We're told about him, we witness the decline of his kingdom, but we never actually see the flawed man. And that makes a difference. Everything we see is Graham not being flawed. Graham is a bigger boyscout than Superman because his red kryptonite moment didn't occur on screen. Also because he's never starred in crappy sequels.
And now a rambling caveat since it will no doubt be necessary. Yes, in KQ1 and 2 you can make Graham be flawed. You can bribe people with treasure and use brawn instead of brain. You can even make Graham do very naughty things like kill a monk or do stupid things like talk to Hagatha in her cave. But those don't count as flaws because they stop you from completing the game in the best possible way, or outright kill you.
And yeah, Lamb, I actually did play KQ5 first on disk. I hadn't heard the voice until years later when I got the whole collection on CD-ROM. But even if I hadn't, you still get a concept of Graham in your head and that includes voice. KQ5 could have given us a jaundiced Graham with a unibrow and it wouldn't have gone against what little detail they've shown of Graham in previous games. But it would have been against how people imagine Graham. The voice is just an extension of that. Josh Mandel sounds like someone's family member to me, not like Graham. And in the world of King's Quest, that's what he was. He was part of the family. For me, he just didn't fit.