This is a pretty close battle.
Johnny's AP is 59.43 tons, while Venus is 47.8 tons. A roughly 1.2x difference. Pretty miniscule. But Johnny has his Super Strength Milkshake, which increases his strength by 800%. Which makes his AP 534.87 tons. The difference would then be roughly 11.2x, which should be enough to overpower Venus' Mid regen and one shot her. Though, I'm not sure what Johnny would open with here.
Venus opens with range attacks and Transmutation, which is used by multiple beams of attacks. Johnny should be fine due to his Acrobatics, Stealth Mastery, and Teleportation.
Venus ethers Johnny in LS. Once she gets a hold on Johnny, he has no chance of escaping, which should give her the win. Though, I don't think Venus uses LS in character.
Venus has Type 8 Immortality, so she will always come back as long as Sailor Crystal is not destroyed or modified. Johnny won't know what Venus' Crystal would unless he kills her, and the only way he can do that is with the Super Strength Milkshake, as the AP difference originally is too small, plus Venus has Mid regen.
Venus' win cons are LS and Transmutation. Johnny's win cons are possibly his Super Strength Milkshake and his equipment. And, if Johnny has no other options left (if the match would even last this long), then his Intangibility and Causality Manip will certainly finish the job.
Johnny definitely has more win cons, it's just that it's unknown what Johnny will open with (though, he'll use the items that will be useful in battle), he won't really take the fight seriously at first, and he only uses Intangibility and Causality Manip as a last resort.
This is all I can think of. Everyone else can probably make their opinion off of this.