I don't think being a leader ups the odds of your skills landing.

If they turn off all cabal powers, he loses imperial defense, tactics, and sigil, all of which he uses regularly. Also he won't have preps, which he also uses regularly, or healing pills. So basically he's a naked STSF h2h/dagger drow with practice daggers. Against, say, any random elf with STSF, he should be on equal footing.

Unfortunately, the requirement that people be naked and use practice weapons will lower damage output, which works to his favor since it means there'll be more time for STSF to charge. On the other hand, he's a naked guy with drow hp, so maybe he won't last that long after all.

The silly thing about the contest is that the practice weapon requirement means that h2h is the way to go for damage. So h2h warriors get an immediate boost. Gnomes/svirf also get screwed, since theirs is the only vuln that can still be exploited. Giants get a bit of a boost, since nobody can bypass resist_physical.

Generally speaking, I'd say the best build would be a giant h2h spec. Not sure about legacies. Probably ward of blades and maybe chilling or the +hp one. Use hands and spam pummel or crushing blow.

However, if I specifically wanted to counter STSF builds, I'd take either another STSF build (since it would cancel out the other guy's), or a combo that can easily blind, for long periods of time. So, whip/flail. And you want to be able to land the eyejab, so probably a high dex whip/flail build. Eyejab the guy early and you essentially remove STSF from the equation. (Assuming it works like I think it does, which isn't 100% certain).