Its a wash. Remember that stone throwers, while slightly more accurate now, also are only S3 and allow saves. So while they hit more you get saves which is about the same for low AS troops, but a huge win for high AS troops.
Cannons wash as well. No guessing, but you still have to roll adjustment and bounce, so it only helps those people that were bad at guessing.
Bolt Throwers work the same, but with more ranks and true LoS they are still very useful.
The only drawback is that you can now wound everything on a 6+, and the wounds are the crew, so war machines are very susceptible to being shot out. You only need to roll 2-3 6's to destroy a machine now.