Are there not still populations that have high carb diets and have very long lifespans and generally good lifelong health as well?
Yes, like the Japanese for example. Nobody knows for sure why this is the case, but it may be a combination of the type of carbs eaten, the rest of their diet being healthy, amount of exercise, genetics, portion sizes, etc.
That still doesn't make carbs good. It just means they have long lifespans in spite of eating carbs. There's no redeeming qualities in carbs compared to proteins or fats.
Also, it should be pointed out that a lot of Asians have pre-diabetes or diabetes....they just don't know it. So the fact that some cultures lead "long lifespans despite eating carbs" is misleading. They are living long lifespans DESPITE eating carbs.
Edit: added some stuff from h1nch and The Shadow from below, thanks.