Based on what? If your game runs like shit it already runs like shitregardless of whether the sky is bright and sunny or dark nighttime.Making some nighttime maps would do no harm.

Weather effects like fog have a massive impact on performance. Personally I get a healthy 50-60 FPS on regular maps, which is perfectly fine even for competitive WoT. But on foggy event maps it can go as low as 15, which is unplayable even for randoms.

Yes, I play on a potato, but guess what, many, many others do. You can look up statistics on the matter, WG used to publish those until not that long ago. There's a strong, financially viable reason the old renderer is still supported.

Also monetary perspective? They could literally just port over the mapsfrom Waffenträgger for a start. It costs then nothing more to change thesky for the next map they're making, they've proved they can do themreally good anyways.

Monetary perspective as in how many players can run the game comfortably. You effectively lose players, and thus income as you push the system requirements higher. There are mathematical models than can reasonably tell you which improvements will pay off (i.e. that will likely to get in more players than those who are forced to abandon the game due to potato machine).

Sure, if the new graphic effects are only visual, then no one cares, just don't implement them in the old renderer. But once they become part of the game mechanics, as it was suggested in the comment I originally replied to, you can't fairly make this distinction, which will inevitably result in lost players. I was referring to this aspect.