Quick Claw is a bad item in competitive because:
- It does nothing 80% of the time
- In practice, it's a bad idea to make your decisions based on a random low % chance
- Even if it does activate, you may not have moved last to begin with
You're almost never going to make a play that depends on Quick Claw working. On the other hand, you can always trust an item like Choice Scarf to hit a speed benchmark or Life Orb to secure an OHKO. You want items with a dependable and useful effect. Quick Claw is an unpredictable luck item.
The only exception is Galarian Slowbro, whose ability Quick Draw stacks with Quick Claw. When combined, it has a 44% chance of gaining priority, which is much better. It's still an inconsistent gimmick set, but at least you can expect it to activate often.