Consider the following:

How would Gen VI fare if:
> Steel still resisted Dark and Ghost
> The plethora of Special moves didn't get nerfed (Draco Meteor, Hurricane, etc)
> Perma Weather was still available

But everything else still remained, so Megas, the Fairy type, and so on? Would it have been any better or worse than Gen V?

Off the top of my head, Pokemon like Helioptile or the Kalos pseudo legend become more viable thanks to their weather based abilities. Aegislash would probably be harder to deal with.