I think it depends on what kind of riding you're doing.

On short fast rides, especially with a group of riders who will drop you if you can't keep up, STI or Ergo shifters give you an advantage that you may need.

But if you're doing long rides, especially if you're setting your own pace, STIs offer little advantage if any. And somewhere beyond 100km riding, they become a torture device. By 100 miles the advantages of downtube shifters are clear:
1. Constantly moving your hands around from shifters to brakes is a great way to prevent the upper body soreness that comes from maintaining the same position for several hours;
2. You use your whole arm to shift from the downtime, not just your fingers. But your arm is a lot stronger than your fingers. As a result, you can still shift down tube shifters when your arm is tired. With STIs there comes a time when shifting is not worth the pain.

That's my experience, anyway.