I don't agree that it is insane. It is less efficient than ideal, but 10gbit over copper is not necessarily dangerously hot or difficult to power.
I have a MikroTik CRS304-4XG-IN on my office desk with three out of four ports at 10gbit and it is perhaps 20 degrees above ambient on the outside. Warm but not hot. Passively cooled design.
A normal Windows laptop runs hotter than that when idle.
I have several 48 port 10G copper switches in my computer room with 40G uplinks. Dell OS9 jobbies. They are a bit noisy, but they don't actually run that hot. I also have some HPE 1G 48 porters and they run roughly the same temperature.
I used to daily drive Gentoo on my laptop. Lovely in the winter!
The cost, power, and length issues meant that it wasn't exactly well-received by the datacenter market back in 2006(!) when it was first released: DAC was the far more attractive option for a link from server to top-of-rack, and fiber was obviously superior (if not plain required) for anything beyond a hop to the next aisle over.
This left an incredibly tiny market, so obviously beyond the initial investment very little effort was put into developing new products for it. So now the prosumer market is hitting the limit of 1Gbps, 2.5GBASE-T and 5GBASE-T (both based on the techniques of 10GBASE-T, by the way) are becoming the norm, and suddenly network vendors remember that box of ancient 10GBASE-T transceiver chips that has been collecting dust in their warehouse.
Aaand suddenly you've got people buying what they think is a brand-new technology, but which is actually designed and manufactured using technology from a decade and a half earlier, and 10GBASE-T gets a bad name for being "hot" and "power-hungry". Turns out it is actually reasonably well-behaved if you actually make use of modern technology!
I expect we'll be using it for quite a while. 25GBASE-T and 40GBASE-T are even deader: A standard from 2016, which a decade later doesn't have a single available product? Mandatory switching to Cat8 cabling - and only a 30 meter range??? And no forwards-looking compatibility? Yeeaah, no thanks.
Right, but for example my fiber ONT only has an rj45 port so I'm stuck using one of these for the link to my UDM Pro. The router and my core switch use cheap DACs.
They're out there. Search engines are just ubiquitously poisoned to the point of uselessness for common terms[1].
But searching for specific gen4 x1 10-gig chips (like RTL8127) does produce some reasonably-inexpensive options for cards with sfp+. Give it a whirl. :)
[1]: I wrote this like it's a new problem, but looking back it may be an issue as old as the hills. I distinctly remember searching for any-brand 10-meg cards with DEC Tulip chips ~30 years ago, because that was the inexpensive PCI chip that actually worked. :)
In your searching did you find any "mainstream" pcie gen4x1 SFP+ cards? I only found the H!Fiber model - which looks perfect, except that our work won't buy from that supplier.
I have a MikroTik CRS304-4XG-IN on my office desk with three out of four ports at 10gbit and it is perhaps 20 degrees above ambient on the outside. Warm but not hot. Passively cooled design.
A normal Windows laptop runs hotter than that when idle.