Steam features never fail to amaze me
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https://programming.dev/pictrs/image/8393f47b-9f61-4601-941f-f4bc8fdb24a8.png?format=webp
https://programming.dev/pictrs/image/8393f47b-9f61-4601-941f-f4bc8fdb24a8.png?format=webp
Obviously not dismissing your experience, just adding my own : I tried it recently on a big game that was installed on my SO desktop, and it worked great. Just had to activate the feature on both Steam instances, restart Steam, and then I enjoyed a superfast "download" speed, that was mainly bottlenecked by my drive speed and even sometimes by my computer's ethernet port limit!
I wonder if I have something set up in steam that is bottlenecking, then. I use my home network to transfer files pretty frequently so I know that's not my issue. Oh well, I don't have limited bandwidth and my Internet is pretty decent so I don't really need it anyways. Glad it works for others though!