Digital Foundry has actual measurements, so whether or not that matches your intuition is irrelevant. But I think the part you forgot is that generating the frames still takes time in and of itself, and you then need to still present those at a consistent rate for motion smoothness.

The Digital Foundry initial impressions are promising, but for me with a 144hz monitor that prefers V-Sync with an an FPS cap slightly below, I'm not sure using 3x or 4x mode will be desirable with such a setup, since that would seemingly make your input lag comparable to 30fps. It seems like these modes are best used when you have extremely high refresh rate monitors (pushing 240hz+).