Sun is pretty bad right now, with Rain rising in popularity, as well as Sand wrecking it. Zard-Y+Venusaur doesn't sound bad in theory, but Charizard being a mega, can't hold the Heat Rock, thus, making Venusaur's chances to set-up lower, and Ninetales sucks balls. For this strategy to work, you have to rely on a free switch into Venusaur, which, with max SpA and Spe, you aren't going to be taking tons of hits. Venusaur also needs LO to hit hard, making it get wittled down quicker. I doubt you can fit Synthesis since Venusaur has 4mss as it is, wanting Solar Beam, Sludge Bomb, HP Fire, HP Ice, Earthquake, Growth, Sleep Powder all at once, so there is no recovery. Also, you miss the main perks of running Venusaur, which is checking a ton of high tier threats, such as Lopunny, Keldeo, Gyarados, Altaria, Azumarill, Manectric, etc. Since you have no Thick Fat and you have much less bulk.
While I don't see the reasoning behind Cacturne and Venomoth still being ranked, Arcanine just comes up into the rankings whenever we have a broken mega steel type in the tier.
tl;dr Venusaur in Sun sounds decent, but there are much better options, both in Pokemon and in weather.