I remember various benchmarks in the years since Maxwell, when they took GPUs with comparable number of cuda cores and clocked them the same, the performance were in the delta of error suggesting that (raw) performance wise you're not getting much more since Maxwell (and that was what, 2013?).

I can confirm you that downvolting can get you the same tier of performance (-10%, which by the way is 3 fps when you're making 3 and 10 when you're making 100, negligible) by cutting power consumption by a lot, how much is that a lot depends on the specific gpu. On the 4090 you can get 90% of the performance at half the power draw, lower tier car have smaller gain/benefits ratios.

Today's hardware typically consumes as much power as it wants, unless we constrain it for heat or maybe battery.

If you're undervolting a GPU because it doesn't have a setting for "efficiency mode" in the driver, that's just kinda sad.

There may be times when you do want the performance over efficiency.