Victreebel is the better sweeper, as is shown by a single calculation comparison:
252 Atk Life Orb Victreebel Leaf Blade vs. 4 HP / 0 Def Primal Kyogre: 190-226 (107.9 - 128.4%) -- guaranteed OHKO
252+ SpA Exeggutor Leaf Storm vs. 4 HP / 0 SpD Primal Kyogre: 158-188 (89.7 - 106.8%) -- 43.8% chance to OHKO
Despite the fact that Exeggutor has a small chance to OHKO 4/0 Primal Kyogre, Victreebel gets the job done 100% of the time against the most common Kyogre and has the added bonus of having Sludge Bomb for Xerneas, and the ability to boost both offensive stats at once in the Sun with Growth.
+2 0+ SpA Life Orb Victreebel Sludge Bomb vs. 4 HP / 0 SpD Xerneas: 296-351 (146.5 - 173.7%) -- guaranteed OHKO
I would recommend this for a basic Victreebel set (you might want to replace Life Orb for Focus Sash in case you run into a bulky Kyogre):
Viktor (Victreebel)@ Life Orb
Hasty | Chlorophyll
252 Atk / 4 SpA / 252 Spe
- Leaf Blade
- Sludge Bomb
- Growth
- Protect
If you're looking for wacky Chlorophyll users then here's a fun gimmick set. Ever heard of the move After You? It makes the target move right after the user. Normally this is kind of meh, but compare the speed boost of Chlorophyll with Eruption Primal Groudon and suddenly you have a game-shredding monster… but be wary, as this set can easily be disrupted by Fake Out, Wide Guard and Primal Kyogre.
Sample Sets
Madeline (Lilligant)@ Focus Sash
Timid | Chlorophyll
252 SpA / 4 SpD / 252 Spe
- After You
- Leaf Storm / Grass Knot
- Helping Hand / Charm / Quiver Dance
- Protect
Groupon (Groudon)@ Red Orb
Timid/Modest | Desolate Land
4 HP / 252 SpA / 252 Spe
- Eruption
- Earth Power
- Flamethrower
- Protect