Question about building quality, in particular London UK.

Hello fellow flight simmers. 95% of my flights end at Heathrow and so I'm very familiar with the approach that takes me over the middle of London, the Houses of Parliament and Buckingham Palace. Those buildings in particular now look stunning thanks to the World Update. However I've noticed that more often than not the other buildings simply don't finish loading in and I'm often left looking down at jagged buildings, pyramid shapes and it's generally a bit of a mess compared to the rest of the experience. For example the closer to Heathrow I get the better the houses look.

I'm running on high settings and have a decent PC so it's not my rig that's holding the game back. Does anyone know what's going on here? Is London simply too dense to fully load in by the time we've flown over it? Should I explore building a high quality local cache file? It feels like the game is loading everything from scratch every time I fly over this part of London which surprises me. I thought it cached everything as you explored the world?

Also, can anyone explain why certain areas look darker than others? Is this down to the type of photography they've used?

It's really not a big deal in the grand scheme of things but I'd quite like it to look it's best if I'm going to see it on a regular basis! Thanks!