Glycemic index is not all it's cracked up to be:

- meal GI can be lowered by simply consuming more protein/fat based foods, or high grain foods alongside the food.

- Studies of GI look at each food in isolation

- GI ignores the insulin index which surprisingly is not correlated that well with glycemic index, meaning there is more biologically at play than simply GI

- Lower GI is not correlated that well with healthier choices

Like everything else, it's not a silver bullet. "Eat unprocessed food that runs, swims, flies or grows" is a simpler diet plan and more likely to be good for us because that's what we evolved to eat, not how quickly does one food in isolation get metabolised compared to 100grams of dextrose.