Grey wasn't bothered about his chances of winning. With his ability, he's certain that he could defeat any of the Seventh stage Sovereigns the Pyro Faction had, he's just curious how he would fare against these people who are regarded as geniuses here. Personally, he didn't rate them that too. Staying inside a secret world their entire life meant that they've not experienced the trials of the outside world, and nothing hones an Elementalist's abilities better than repeatedly being in a life or death position.
Grey didn't think any of these people have genuinely been in a life and death position. People can get injured during sparring sessions, but they rarely get killed, unless it's on purpose, or an accident.
