Anyway, while we're on the subject of why Rockstar sux, can you explain what's wrong with GTA4's "LoD meshes"?
This is probably completely wrong, but it's been so long since I read up on the technical info from the modders...
IIRC, Rockstar didn't simplify their LoDs enough, and the game uses high-LoDs at a much further range than it should, leading to too many drawcalls which slows down the rendering time. If Rockstar had toned the ranged down and made LOD3s instead of just 0s (highest quality), 1s and 2s (supposed to be mid-range, I believe, although I could be wrong, that many open-world games use 4 LoD levels to gain finer control of memory management), then likely the game performance on Day 1 would have been significantly higher and there would be less complaints.
Also, the game loads chunks of the map at any one given time which is normal for these kinds of games, but the maps themselves aren't optimised and don't contain LoDs, only the objects do. How they managed to pull off loading large chunks of the game world when flying is a mystery to me (probably a simplified mesh that I haven't seen in the game files).