Surviving an assassination attempt isn't a feat, nor does it qualify a good leader.
He started a rebellion only after surviving an assassination attempt (He was no longer facing the "Threat of Death" for treason) I don't see how that qualifies him as a good leader (For the record, any Horde leader could have assembled the rebellion, thanks to Garrosh, not Vol'jin's own Political games.)
He retook the Echo Isles while:
The Orcs Had their champion lead a War against the Qiraji, sent expeditionary forces into Outland, Waged a War in Northrend and secured their borders.
The Tauren mended Night Elf:Horde Relations, expanded southwards to Grimtotem territory, secured their borders, helped out in the Orcish leg of the Northrend Campaign.
The Forsaken built up a superpower in a matter of years, fended off attacks from the Scourge, Scarlet Crusade and Alliance, sent troops along with the Orcish expedition to Outland, waged their own battles in the Horde's Northrend campaign, the Forsaken, however, also suffered a coup.
So all in all, what has Vol'jin done to help the Horde? He secured the Echo Isles? That's not an accomplishment, it's pathetic that the only thing he and his people have managed to do are piggyback off from Orcish Campaigns (His greatest feat in outland was Zabra'jin *ooooh*), direct artillery at the Battle of the Undercity (While Thrall and Sylvanas did the actual commanding.) send a token force to Northrend, while the other races are deployed in full force to face a world ending threat, because he's taking back some islands that slipped from his grasp.