Except for the Pico (which is very different from the full RPi), you could do all that with a mini-PC.
There are certainly usecases, especially using the RPi's low-level IO, where that's not possible, but as you yourself have shown, people do often get into situations where they are competitors.
Probably shouldn't have your decoder in the attic anyway, as they aren't well suppressed in terms of EM interference which will seep into the antenna. Particularly a cheap AC-DC wall wart, they're basically broad-spectrum noise-jammers.
I shunt the USB output of the SSR dongles onto Ethernet and pipe that to the PC downstairs.
Huh? It’s ADSB 1090 MHz on a short run of coax to a FlightAware SDR USB dongle. It’s an urban environment so I don’t expect much but I receive plenty of aircraft over 300 nm. Any further away and I would have loss due to inherent limitations of the coax. I could go with like LMR400 but I am not going to spend that kind of money or add like a LNA. This is a setup people commonly use
There are certainly usecases, especially using the RPi's low-level IO, where that's not possible, but as you yourself have shown, people do often get into situations where they are competitors.