This is super obvious to gamers if they pay attention. I can (and often do) sit there and watch a game update download on Xbox at 87 mbps, then jump to 178mbps, then drop to 112mbps. Then I download an update on Steam that rips down at 300mbps.
It's the same principle that people have failed to grasp since the days of DVD players. They go buy a DVD player and then complain the quality is no better than the VCR...........never realizing they are watching it on a wood cabinet tube TV (usually with coax inputs lol) that can not display the higher quality. Happened when 4k came out but in reverse. Why doesn't my TV look better, I just dropped $4000? Um, because no one is broadcasting or streaming 4k at the time? lol
A connection is only as good as BOTH sides, and the connection.
The benefit to a Gig line is not single transfer speeds, it's the bandwith that comes with it. Sure, you can't grab a file from Xbox at 1gbps speeds because their servers and bandwith are not going to be Gig dedicated to each customer, but you can grab multiple files and stream on multiple devices at once up to that speed.