That's not the complaint. The complaint is that dragons are emptying out the major cities because they level with the player while the NPC guards in those cities don't level.
I see. I still see no problem with it, though. I don't know at what level this issue might become more evident, I'm level 44 and guards still defend themselves pretty decently from dragon attacks. Plus, like someone else mentioned, dragon attacks may be common, but dragon attacks in major cities are rare. In more than a hundred hours of gameplay I've only had two dragon attacks in cities or towns, and never inside. In fact, I didn't even know that could happen until I started reading people saying that they lost blacksmiths.
But either way, I think there really is some people suggesting that dragons shouldn't attack towns at all, or that some NPCs should be invincible. Then you have others next door complaining about that exact thing. Personally, I think the way Bethesda handled the situation is mostly fine. I like that certain NPCs can't die, otherwise it would be really frustrating to get into a swordfight with five Deathlords in a narrow corridor, and see how you failed a quest because there was no way in the world that any NPC could survive such match.
Then with the dragons is the opposite, knowing that they can kill anyone around is precisely what makes their attacks exciting. If it was just a fight were everyone is safe, what the heck would that matter?