I'm working on a mod to change the difficulty levels in the game right now. I've started by making all intermediate level AI times a little slower and Professional AI times slightly faster. I've also increased the legend AI times in Monza, as this was not at 100% level.
If anyone wants a mod with changed difficulty levels of AI times let me know. Also let me know whether a particular difficulty level should be made slower or faster. By the way it is impossible to make Legendary difficulty any faster if that's what you want, but I can make Expert difficulty faster or slower depending on what people would like.