cool topic...thought a lot about this. Long before ENT ever aired, I always squared the Praxis issue in a different way. ENT actually helped buttress the case I think.
We first saw Qo'nos on TNG and it looked like this:
So ~70 years after TUC, the homeworld is gritty and always dark and hazy. The smog seems to hover over their buildings...and it's never sunny. Also, despite huge outdoor walkways that criss-cross through their cities....they're entirely empty. No Klingons walking or even standing around outside...anywhere. Intense pollution and little outdoor activity....these depictions of Qo'nos would be entirely consistent with a world that was still experiencing the long-term results of a planetary atmospheric disaster....like the Praxis explosion.
If it would have ended here, the explanation would have worked fine. We never saw an outside shot of Qo'nos during the TOS era (iirc), so there was nothing to compare it against. After Praxis, maybe the Feds helped in some way to offset the most dire ecological scenarios and the Klingons learned to cope with a newer, more harsh environment...allowing them to stay on Qo'nos.
But then, along came ENT's depiction of Qo'nos:
This strengthens the story imo. So, 200 years before TNG --and over 100 years before the explosion of Praxis in TUC --Qo'nos has blue skies and sunny days. We see a lot people outside doing all sorts of all things. This seems to be a healthy ecosystem....before the planet-wide disaster of Praxis.
These differences could be explained by many things other than a planetary environmental change...but DS9 helps out here.
Qo'nos in DS9....as compared to Qo'nos in ENT:
The color of the planet's atmosphere significantly changed over the course of two centuries. The Praxis explosion explains the atmospheric difference.
It's not canon of course. And this has never been explained on-screen...no doubt because the story was never meant to be a coherent whole. But it makes sense to me this way. The Praxis explosion works to account for these two different depictions. If you accept something alone these lines, the events of TUC tie things together pretty well.
I always saw the different depictions (at least on the planet's surface) as just being different areas of the planet. Compare Egypt, India, New York and Iceland. Same planet, different look. Klingons like to fight amongst themselves a lot, so I can easily see the "capital" moving to the territory of whoever's running the planet at the time.
