For the competitive games where higher framerate is most advantageous (i.e. shooters), I come to the opposite conclusion. Games like that tend to have long periods of low activity where you aren't being challenged, with short periods of chaotic fighting where framerates are significantly worse. It's only during those chaotic times where the performance (of both the hardware and the player) actually has an effect on the outcome of the match.

I think it's far more important to have a consistent framerate than it is to worry about wasting potential (fast) frames. Inconsistent smoothness and input lag will create a disadvantage compared to just playing at a capped (lower) framerate.

So I think a balanced system (both the hardware and the graphical settings) with a 144hz monitor should be able to run games at far beyond 144 fps most of the time, so that the framerate will only drop down to around 144 in the worst moments. I would even suggest setting a framerate limit near the worst framerate your system often drops down to in the game.

How much your hardware needs to be "overprovisioned" depends on how poorly optimized the game is. For many games this can as much as a factor of two difference. So you might only be putting 50% load on your GPU most of the time, but peak at 100% load at important times.