Sorry you had a rough experience! My rental experiences with National have mostly been 100% smooth and easy, so I can empathize with your experience that any hitch in the process is disappointing and disruptive.
With that said, my answer to your question is clear, and reflects most of the other commentary in the thread: "Fagetabbit and be thankful there wasn't anything seriously wrong with the car!" Yeah, it was inconvenient for you -- but screwups happen occasionally in any business, and it sounds like National not only took care of you in a meat-and-potatoes kind of way (you got a working car without too much hassle or delay), but went above and beyond their policies (allowed an exchange at an Enterprise, which is in fact a separate company even if it's part of the same family of businesses).
What I expect from a National rental is to get a clean, safe, functional, moderately comfortable car that gets me where I'm going, with minimal time wasted at pickup and dropoff. What I hope to get (and often do get!) is my choice of premium or even "cool" vehicles. But that's above and beyond. And when I get a little less than my expectations (e.g., have to do an exchange, or get stuck with a truck or minivan)... yeah, I'm not happy, but I match those rare experiences up against the many upgrades that I get, and call it a win overall.
So, IMO (and since you asked!), what you had isn't a bad day. Just an "eh, some days are better than others" day.