The guide should be updated. I have already come across things 2 - 3 times that are no longer necessary. Among other things, playing a Rattata at level 80 so that I can enter the Hoenn region. I just happened to be told today that this is no longer necessary. So far I've put 4+ hours into leveling it. That was a very annoying realization for me that it's no longer necessary since I was just following the walkthrough.
Thanks in general though for all the work put into the guide.