Well, Avengers: Endgame finally gave me a worthwhile answer.

Three children and a wife – gone with the snap of a finger. All that remained was a man, lost in his own grief; his moral compass reduced to dust both instantly and (seemingly) irrevocably. It’s enough to send anyone over the edge – Avenger or otherwise. And that’s exactly what it did to Clint as he spent the next five years physically dishing out the pain he was feeling emotionally; burying his sorrow under heaps of dead bodies. It was, without a doubt, the darkest we have ever seen one of our heroes been – but given all that he had lost, it made a lot of sense.

Clint loved his family – so much, in fact, that he decidedly kept them a secret from the other members of the Avengers (except Natasha, who knew prior to their joining the Avengers). Much like superheroes keep their identities a secret from the general public for their own safety, Clint kept his family a secret as well; and with all that’s happened to Pepper Potts, Jane Foster, and Betty Ross as a result of people knowing their respective heroes identities, it makes sense that Clint would want to ensure that his family was kept safe. As Adrian Toomes might say, he played it very “close to the vest,” – even keeping it from his teammates, who, at this point, had essentially become like a family to him.

All of this is to say that, when we first lay eyes on Clint in Avengers: Endgame we can see that he’s a far different man than the one we saw during the films opening scene. And, while, granted they’re all different from who they were, his transformation is the most jarring. All of the Avengers have killed – we’ve seen that it is an unavoidable part of the job – but none have sought out violence in the same way Clint had. In many ways the MCU’s take on Ronin is very similar to that of Frank Castle; a man hellbent on dishing out his own brand of justice after watching his family get murdered. If you slapped a skull on his chest the two would be practically indistinguishable from one another, given all of the carnage that surrounds them each.

However, unlike Frank Castle - who has no way of bringing back his family - Clint is given that opportunity, as Natasha informs him that they have finally found a way to fix what Thanos did. While reluctant to “hope” again, he decides to put his faith in Natasha and the Avengers and rejoins the team, albeit still unconvinced as to whether or not their plan will work. It is not until he travels back himself and hears his daughters voice again that he appears to have returned to the Clint we’ve always known.