I've tried to use Weezing again, and it does have things it can own, but the fact is that it can't really touch things like Heatran or Reuniclus, and doesn't have the firepower to threaten many other things that its best option against them is Will-o-Wisp. Weezing would benefit from an evolution with a Electric secondary type haha. Anyways, Haze, Pain Split, Will-o-Wisp and a couple of attacks are about the extent of what Weezing can do. Gliscor has many more options/assets like Poison Heal + Toxic Orb to allow for healing and/or stalling with Toxic and Protect as well as status protection, Swords Dance, STAB Earthquake (and the occasional Acrobatics should you choose), usable speed with Taunt. Besides, it has less physical bulk than Gliscor due to less base HP and defense, so it's not exactly taking Excadrill's +2 Returns (or Rock Slides) any better.