It's inherently worse than anything fibre, or even DAC cables (which are kinda cheating.) It needs a shitton of analog "magic" to work with the bandwidth limitations of copper cabling.
DAC cables are cheating because due to the extremely short range limits (5m, 7m if you're very lucky) they can just put the 10Gbase-R/SFI signal straight on a pair of Copper at 10.3125 Gbaud.
10Gbase-T, to try to get to 100m, throws FEC on it and converts the signal to 4x PAM-16/THP at 800 Mbd, and then uses 4 copper pairs *bidirectionally*. That's the analog magic.
Okay. Sure. But why do we notice that on 10GbaseT and on 1? Is there some signal processing which is exponentially expensive at faster speeds? I’ve seen cards using 25W per port.
Yes, that signal processing is massively more expensive. A 10Gbase-T PHY is a sophisticated DSP. Not sure if the power needs are exponential, given we only have a few data points, but it's in the ballpark.
(1000base-T PHYs are already DSPs, but nowhere near as sophisticated)
To be fair, the power consumption is also my biggest gripe with my WiFi 6 AP, they run extremely hot.