When you gave me this team last week, I knew you'd RMT it, so I did some extensive testing. Before though, I just want to say that I love the idea to have a defensive pivot like Lanturn on an extremely Hyper Offensively based team. Volt Switch especially works wonders when trying to switch between sweepers without taking damage. However, like you said, Venusaur "can be annoying," as well as other Sun sweepers, like Victreebell and Sawsbuck.
Life Orb Venusaur especially.
It's able to OHKO 4/6 of your team if it's the most common variant (Giga Drain + HP Fire) by hitting Genesect while if it's the HP Ice variant, it can OHKO Landorus instead:
252 SpAtk Life Orb Venusaur (+SpAtk) Hidden Power Fire vs 0 HP/4 SpDef Genesect: 134.28% - 156.89% (Guaranteed OHKO)
252 SpAtk Life Orb Venusaur (+SpAtk) Giga Drain vs 0 HP/4 SpDef Keldeo: 99.38% - 117.03% (93.75% chance to OHKO)
252 SpAtk Life Orb Venusaur (+SpAtk) Giga Drain vs 36 HP/220 SpDef Lanturn (+SpDef) : 65.25% - 76.5% (2 hits to KO) - Lanturn can't do anything anyway. It's pretty much set-up fodder. If Venusaur comes out on Lanturn, it's game over with a single Growth.
252 SpAtk Life Orb Venusaur (+SpAtk) Giga Drain vs 0 HP/4 SpDef Terrakion: 99.38% - 117.03% (93.75% chance to OHKO)
252 SpAtk Life Orb Venusaur (+SpAtk) Giga Drain vs 0 HP/0 SpDef Landorus: 55.49% - 65.2% (2 hits to KO)
252 SpAtk Life Orb Venusaur (+SpAtk) Sludge Bomb vs 0 HP/0 SpDef Mew: 51.91% - 61% (2 hits to KO)
I probably didn't have to do those calcs, but as you can see, 4/6 is indeed OHKOd while the other 2 are 2HKOd. That means with prior weakening of Landorus or Mew (which is a suicide lead anyway), Venusaur doesn't even need a growth to sweep flat. Victreebell is even worse because it has access to a Hidden Power of its choice, usually HP Ice (since Weather Ball serves as its Fire coverage). That means once Mew is taken down, it's over.
To help alleviate the Sun problem, I recommend you try a temporary weather move on either Mew or Lanturn. Most Sun teams view their Ninetales to be useless fodder once the Sun is permanent, so they do actually sac them. You can take advantage of this by trying Hail over Tailwind
on Mew or trying to fit a spot on Lanturn, probably over Rest and Sleep Talk (but that would ruin your amount of pivots). If you do choose Hail on Lanturn, I'd add Thunder Wave as well. Since Lanturn doesn't die to Venusaur's Modest LO Giga Drain, it can massively cripple the opposing threat, allowing all of your Pokemon to take it down. Even though Rain slightly benefits your team through both Lanturn and Keldeo, I feel like removing opposing Rain would take a burden off of Lanturn as Tornadus-T won't be as free with its Hurricanes. Of course, it also removes Sand, so Stoutland or the new-popular Sandslash are less of a problem.
But most importantly, it removes Sun, pretty much rendering Venusaur an easy Pokemon to deal with. If you do go with the Hail Mew route, it wouldn't be able to just explode at the beginning of the game, so that could be a bit of a problem (especially if your opponent is very careful with their Ninetales). Lanturn is bulky and sticks around, so I'd go with him instead.
It's not only Venusuar, but in general, grass typing. Genesect is your only resist but it's pretty frail considering it has a -Sp. Def typing. Virizion is a bit of a problem as well, causing you to rely on Genesect for resistances. Obviously, it'd have to win 2 Speed ties to OHKO both Keldeo and Terrakion, but knowing your luck, it's definitely possible. Genesect can't exactly come in on a Giga Drain or Leaf Blade because of Virizion's other STABs (Focus Blast/Close Combat). You pretty much have to fodder something every time it comes in or play insanely risky vs Virizion to beat it. It's a good thing it's uncommon lol.
Anyway, there doesn't seem to be any other massive problems from what I've seen when using the team, so that's it! Obviously, this team is amazing (and extremely fun :]), so great job!