I mostly agree with you.
But in the particular context of "messing up" by giving an NPC a particular ability score or other fundamental trait and then having it cause ripple effects all through the character, I'm not sure that there's much worth learning there. The only thing you'll learn from that is a lesson like "races with level adjustments can be really screwy, pay extra attention." That's a good lesson of the same kind as the lesson, "When riding your bicycle on the Autobahn, make sure to wear reflective clothing." Good advice, but better advice might be to stop doing that.
The lesson I learned from making NPCs in 3e was to stop making NPCs in 3e and start fudging their stats. Then 4e came along and agreed with me.
But in the particular context of "messing up" by giving an NPC a particular ability score or other fundamental trait and then having it cause ripple effects all through the character, I'm not sure that there's much worth learning there. The only thing you'll learn from that is a lesson like "races with level adjustments can be really screwy, pay extra attention." That's a good lesson of the same kind as the lesson, "When riding your bicycle on the Autobahn, make sure to wear reflective clothing." Good advice, but better advice might be to stop doing that.
The lesson I learned from making NPCs in 3e was to stop making NPCs in 3e and start fudging their stats. Then 4e came along and agreed with me.