So what is worse on the 5dm3 compared to the 5dm2

Well, your 3 biggest considerations are all exactly what the Nikons are better at than the Canons so I'm not sure why you want to switch. I doubt the autofocus issues are that bad on the D800 and if you are doing landscapes you should be manually focusing anyway. If you did switch I would say that the 5D2 would make more sense if you didn't need the top-notch AF system on the 5D3. You could take that extra money and invest in lenses.