A) No. A better way to handle this without ruining the fact that they're meant for 50/60/70 content respectively would be SE simply making them sync a player much like FATEs do. Adjusting mob values would be far worse when there's already a system in place to adjust players.
B) A ranks are short already. They're fine I'd say. S ranks could stand to be a tad shorter or simply make their random timer within the capable spawn time an exact time frame.
C/D) Unnecessary.
How your hunt experience goes will vary with each server. Some of them don't have established Linkshells or groups dedicated to keeping up with these or sharing the info. Some do. On Leviathan it's very easy to farm A ranks and even S ranks. I only play a few hours a day and I can farm 1-3 dozen A ranks daily. We have several completely full Linkshells dedicated to spreading the info and tracking them.
Personally, I find the only major drawback to the Hunt system design is that 1 player can often ruin it for others. Be it by off setting timers, early pulling, etc. This seems to only be an issue for smaller/dead or less active Hunt servers though.