This game isn't all about who's X rank on the leaderboards. So in all fairness, why does it matter if there is a joint leaderboard?
Also, if I were to look up my own rank, I'd like to see where I am in my server, and then how that compares to the other server. Surely it would motivate you more to try and catch up someone who's ahead of you, even if they play reboot and you're on a regular server...?
I know for sure, that as and when I grind, I'd look to race a few reboot players around the same rank. And then see whether I can sustain a grinding habbit to progress up the ranks.
So yeah, I'm in favour of there being a joint ranking leaderboard, just as there is now. There's nothing wrong with how it works at the minute, and people are just whining because they're salty that reboot server players can gain exp faster than regular server players. If you're really that concerned about your non-reboot rank then click the non-reboot button.
