No, it does take WX, turbulence, airspace restrictions, etc into account, but it isn't perfect yet and you do need to take it's suggestions with a grain of salt... but has improved since we started using it last year. The AI engine is built to have the flight avoid planned echo tops, not base or composite reflectivity, so the margins are a lot closer... I have had some success with it, but it is close.
As for the time savings, I don't agree that the dispatcher doesn't have time to check actual vs. planned times... unless there is a lot going on there is time to do this, you just have to want to do it! The problem is that a lot of crews, especially on the longer routes, still think that taking the direct from Ohio to the arrival on the west coast is going to save them time, and we haven't convinced everyone to stick with the planned routes yet so they aren't flying what is on the paperwork... hence we really can't make comparisons.