What were the circumstances in each case? Because I recall two and both were extreme.
Example 1: "Yesterday's Enterprise"
The Enterprise D loses it's shields and is fired on repeatedly by two Klingon Birds-of-Prey.
Example 2: "Star Trek: Generations
A Klingon Bird-of-Prey gets the shield frequency and fires through the shields, rendering them useless (why they couldn't modulate shield frequency, who knows), causing sever damage.
Both instances don't show a bad design but rather a ship in abnormal distress. One wasn't lazy writing, the other, well ... make of it what you want.
Example 1: "Yesterday's Enterprise"
The Enterprise D loses it's shields and is fired on repeatedly by two Klingon Birds-of-Prey.
Example 2: "Star Trek: Generations
A Klingon Bird-of-Prey gets the shield frequency and fires through the shields, rendering them useless (why they couldn't modulate shield frequency, who knows), causing sever damage.
Both instances don't show a bad design but rather a ship in abnormal distress. One wasn't lazy writing, the other, well ... make of it what you want.