Benchmarks are like the SP500 index or IQ measurements: They distil multiple variables into one number. In doing so you lose details, but do get a useful measure.
Yes, they are imperfect, but they do broadly measure how fast a processor is, and can be used for comparison.
Every PCIe 10G ethernet card I've seen has a heatsink on it, sometimes covering the entire card or even have little fans on the heatsink.
Expecting it to work full time in a laptop is a bit of a stretch of the heat dissipation budget.
Also, the laptop he is working has the AMD FP8 chipset - depending on how the ports are setup, he might only get 10G USB, if the ports are allocated to video instead.
A lot of this has to do with segmenting the market into high-end and low-end products.
When they were the underdog to Intel, they gave away lots of premium features to beat Intel.
Since they got more popular, AMD has been taking away features, or not upgrading old tech, from their desktop/gaming CPUs: Their DDR5 interface is gimped, being slower than Intel now, and still limited to dual channel. Their chipset link is still PCIe 4x4 the same as two generations ago.
If you want these features now, you need a server product.
Microsoft is also doing this, Microsoft Authenticator, no longer works under GrapheneOS for corporate creds, and coming in July they will delete any Entra-related IDs from your phone.
This sort of thing really annoys me. Part numbers are for use of engineers, not for the marketing dept. If you change the specs, change the part number.
https://en.wikipedia.org/wiki/Sopwith_(video_game)