I also understand them and reasons are not lame but probably very valid.
Too much variables, too much data clusterfuck and too much different options.
I agree how Premium-only/stock tires/SRF disabled leaderboards would be great, but than the backslash from Standard-lovers/tuners/RaceSoft Afficionados/assisters/etc would be unbearable.
This way we have new leaderboards every few weeks (Seasonal Time Trials) and everybody is more-less happy.
Too problematic, I hope GT6 will offer some solution for this under Arcade mode (Simulation mode would be very problematic due to Vehicle Evolution process).
Not a lame reasons.
Option A:
FF/FR/4WD/MR/Open Wheel
Option B:
Leaderboards for car class types like GT300/GT500/Nascar/WRC
Option C:
Two leaderboards for each car, Stock and Tuned
Option D:
The game gives you the car, kind like GT3 Time trials
Option E:
Mantain the leaderboards from Prologue, just add the extra ones for the Premium cars
And the options could go on and on...
I know everyone is going to point at 1000 cars being the problem, but it shouldn't be. There are a number of ways to solve a problem to give us a feature that greatly increases game value. I still can't believe they put the Top Gear test track in it and we can't do power laps to compare cars and drivers online (this doesn't mean they had to include the Stig).
I know i'm not the only one and in fact in years two and three of owning the game i can say that i enjoyed Prologue more than GT5 just because that.
I hope they are listening and taking notes with the seasonal time trials, which are mostly a dash to find the money car of the week so that they can adjust these things and give us some leaderboards on GT6.