I'm afraid I can't quantify it for you, but subjectively I'm completely confident that using a high end fitness tracker for training and racing makes me faster in triathlons. Other than that I'm not interested in trying to measure efficiency with versus without the device as that would be a total waste of my time.

This could be pretty easily quantified if you look at how world records have progressed over the years.

Better fitness technology leads to faster times across the board.

Technology has also improved in many other areas: exercise physiology knowledge, nutrition, aerodynamics, lab testing, PEDs, bouncy shoes, etc. It's tough to isolate how much of the total improvement was caused by fitness trackers.