>>20176944First off, Ninetales is really, really shitty. Its only redeeming factor is Drought. In every other aspect, it's extremely mediocre.
Now, sun would be okay, if there were any good sun abusers. There are some, but most have serious issues in the meta, whether it be not being powerful enough to break through stall (Chlorophyll sweepers) or not fast enough to sweep offensive teams (fire types. Oh and a lot of them are walled by one or the other of bulky X-zard and Chansey.) This is opposed to Rain teams, who have two in one with Swift Swimmers, i.e. Swords Dance Kabutops and Specs Kingdra (or just go for fucking broke and use Specs Omastar.)
And the Chlorophyll sweepers also have some issue with offensive teams, namely things like Aegislash, strong priority users (cough talonflame cough,) Charizard, Mega Mawile, Mega Pinsir, and so on. There's just too many problems sun teams have to overcome, to the point where building a good team that's dedicated around it is borderline impossible.
tl;dr Ninetales is shit because sun teams are shit, and if you want to use one of the very few good sun abusers, you're better off with Y-zard or a manual sun setter, because Ninetales really is shit.