Both Scizor and Scyther are powerful pokemon and despite Scizor being Scyther's evolution, they share the same Base Stat Total.
While Scizor gains a strong defense and has its weaknesses reduced to a single 4x Fire, it sacrifices speed, neutralizing its sweeping capabilities without a priority move.
Scyther is cursed with a 4x weakness to rock and 4 weaknesses to common types. However, it has access to Eviolite, which boosts its defenses beyond that of Scizor. It also maintains a 105 Base Speed, enabling it to sweep through a number of other pokemon. And with Technician, Scyther can be a humongous threat.
Scyther's new bulk also enables it to be an effective Swords Dance, Agility, or Substitute Baton Passer for added versatility.