1) It's not the UFC's scoring system. It's the scoring system laid out in the Unified Rules, which have been adopted by every state that sanctions MMA.
2) It's not confusing if a) you follow the sport and b) the judges on a given night actually know what they're doing. The criteria to win is based on effective striking, grappling, aggression, and ring/cage control. The winner of a round gets ten points, the loser gets nine or less. As long as a judge is actually aware of what constitutes "effective striking", etc, it's no mystery.
3) Yes, the system needs to be changed, and the Pride system would help. However, more than that, they need judges who know what they're doing. Many judges have no clue about the grappling aspect of the game. You can implement any kind of scoring system you want, but until a judge can recognize the difference between an triangle choke and an arm bar, there will still be crap calls. Overall, though, they seem to be doing a good job.