Sceptile isn't always a better sweeper. Virizion has a few perks. Virizion has slightly higher base attack, 90 compared to Sceptile's 85. Virizion also has more defense, 90/72, as opposed to Sceptile's 70/65. This means Virizion has a much higher chance of surviving priority attacks, like Extremespeed, Mach Punch, and Bullet Punch.
Most importantly, however, Virizion has a better offensive STAB combination, as well as the ability to fit all the coverage it wants on one set. Sceptile only has Leaf Blade for STAB, which doesn't help it in UU, leaving it walled by Bug, Steel, and Flying-types alike. Virizion has a secondary STAB in Close Combat, which nukes Steel-types. Sceptile is forced to choose between Earthquake, Rock Slide, and Acrobatics in the last 2 moves. If you're using Acrobatics as you suggest, you need to pick between the other two. using Earthquake leaves you walled by Crobat, Zapdos, and Togekiss. Using Rock Slide leaves you walled by Registeel, Cobalion, and resisted by Bisharp. Virizion can run both Close Combat and Stone Edge to hit all of these pkmn on one set.