Jolteon actually isn't a huge threat to his team, it's a threat, but it's not a auto-win.
Jolteon does 78.7% - 92.7% to Thundurus with HP Ice, which is a KO after Stealth Rock, Thundurus does 82.4% - 97.1% to Jolteon with HP Ground, which is a KO 61.90% of the time, after stealth rock. So in a...