I completely disagree with this statement. On paper, nasty plot looks better, but with base 100 speed, its not. This is the same issue with Tail Glow Manaphy vs. Calm Mind Manaphy. Sure +2 spatk is nice, but you're open to being revenge killed by Pokemon on either side of the attacking spectrum. With Calm Mind, Celebi becomes significantly tougher to take down specially, meaning that its much harder to revenge kill.
A lot of people will say that Calm Mind Manaphy was scarier than Tail Glow Manaphy, even though Tail Glow is now +3. I'm not saying that nasty plot shouldn't be mentioned, but a more conservative stat boosting set should be added.