Hiei stands no chance at the level he was at during the tournament. The dragon boost was nice and definitely more powerful than Bui. But Toguro specifically teased Bui. Made him think that he was close. Maybe Hiei with the absorbed Dragon takes Younger Toguro at the fake 100%. But doesn't come close to Toguro's actual full power.

To use stuff from the series, Toguro was a low A class demon. It was super surprising when everyone got to that level fighting after Yuske died. It wouldn't be that surprising if Hiei was actually as powerful as Toguro during the tournament.
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I'm the Pez and I'm AWESOME

Hiei with the Dragon of the Darkness Flame absorbed vs Younger Toguro (100%)

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