DxD definitely has deconstructive elements. I feel like "a deconstruction" sounds a bit too big and too absolute - but some elements are definitely there.
The biggest one for me is without a doubt Issei.
Usually, there are exactly two types of male MCs:
Either: they are a strong, confident stallion and always know what to do.
Or: they are a bumbling idiot that is barely able to stay alive without extensive care.
In the west we have Commander Shepard, Geralt or any action movie hero on one side and Homer Simpson or generally any male lead in a comedy scenario on the other side.
In Japanese media (especially manga, anime and LNs) we have Goku or Gon on one side and Yuuki Rito on the other side.
Between those two extremes is an eerie emptiness. Most of what you find in there are children (who in media much as in real life often are not seen as humans...) that want to grow into the badass stereotype (and usually succeed in doing so) like Simon or Bell-kun. They hate their weakness and cry a lot in the beginning but they stop doing so eventually.
Issei... is different.
He is unpopular and weak. But he still does badass stuff.
And while he cries in the beginning like a badass in the making, his ultimate goal is not becoming strong to be a hero.
Instead, his goal is being surrounded by breasts. He fundamentally wants to stay like he is and enjoy the things he enjoys. He wants strength not to fill a predefined form of badassery but instead to forge his own form.
And this is rare. Nearly unheard of.
You either have strength and are "a real man" or you are a loser.
Even side characters fill this role! Know the tech guy from any action movie in recent memory? He either is a complete joke that fails at everything he does and risks the whole operation or he is able to give you a ton of technobabble while hacking the FBI and CIA at the same time.
Those are the rules!
But Issei doesn't follow the formula. And instead of making him an anti-hero or even a villain, Ishibumi makes Issei the MC. And gives him a harem.
To answer your question:
"Does it take a simple and devoted, yet naively radical, individual to help us recognize our own humanity?"
Yes, yes it does.
Issei sees that he is weak.
In the beginning he hated this weakness. But after being told time and again that he is the weakest host in history he has accepted it. Other than Simon or Bell I don't think he hates what he is but uses it as a base for growth.
Issei likes boobs. A lot.
But he does not want to live in a world in which he does not love boobs. The dislike of others and even his own death could not erase the simple truth: He likes what he likes.
And yes, this made me question what I really want in my life. Do I really want to be the badass that is always right even if he is wrong and that basks in the glory of others. Or do I simply want to be me.
And after some thought it made me realise: As long as I am human - a thinking and feeling being - I will only be able to achieve one of those possibilities...