In fact, by the end, you could argue Welling had a greater grasp and understanding (and thus respect and appreciation) for his power than any other on-screen version of the character because he had to fight so hard to "earn" it.
I didn't see it as fighting to earn his power -- more like stubbornly resisting his responsibility. It wasn't until season 8 that he really accepted his power and chose to become a superhero, and even then he went about it pretty gradually. It was more something he had to be talked into than something he strove for. So I don't find it the least bit implausible that he gave it up.
Anyway, it's been a decade since we last saw him. A person's priorities can change in a decade, especially if parenthood comes into the picture.
Hmm... Earth-38's Superman was willing to leave Earth to start a family because he trusted Supergirl to keep it safe. What was the status of
Smallville's Supergirl at the end of the series? Or in the "Season 11" comics? As far as I know, she was still around, so maybe that Clark made his choice for a similar reason.
I just take the Routh Superman as a broad stroke who's supposed to represent the Superman Returns version and the Reeve films version (now with elements of Kingdom Come mixed in), without getting nitpicky about how that works continuity-wise.
Well, the
Returns version was itself a broad-strokes approximation of the Reeve version, so I have no problem accepting this one as the same character Routh played before. And it's been 13 years since SR, which is plenty of time for the KC-like events to happen in the interim (along with the
Superman III-like events of going nuts and fighting himself). After all, SR was the only story we've previously seen in that continuity, so there's plenty of room in that reality for everything established here to have existed/occurred there.
Well, I suppose one discrepancy could be the appearance of the
Daily Planet building. Presumably the interior was rebuilt after the Joker attack (I think they redressed the CatCo sets), but did the exterior, or the cityscape beyond, look anything like the one from SR? Well, any difference could be chalked up to artistic license and available digital assets.