Anyone trying to use a GearScore-esque addon in Classic will be broadcasting to the entire server that they have no idea what they're doing. The stats on an item mattered far more than the item level in many cases--for example, just about every raid wants someone carrying Nightfall for its spell damage taken proc, Edgemaster's Handguards, a mid-level blue mail item, was one of if not the best gloves for Fury warriors due to the extra weapon skill, and resist fights often involved getting trinkets off mid-level bosses and crafted gear well below the power of raid drops so you could resist incoming elemental raid damage.