Nobody uses 1Gbps. Nobody. Not download, not upload.
I did work for an ISP that served a lot of video editing shops, and I could see them potentially using >1Gbps at night, when they upload all their video to the cloud. They are one of the few customers that I have seen saturate 1Gbps.
Most people don't realize: your bandwidth is fine. Your latency is bad. Latency has so much to do with the internet experience.
You can have 20-50Mbps in a household with two parents and two kids, and your internet experience will be great if your latency is great.
There are three factors that determine the quality of your internet experience: 1) bandwidth, 2) latency, 3) packet loss. In practice, #3 is not usually an issue. But every ISP only advertises #1.
When you get introduced to fiber, the biggest upgrade you get is in latency.
So you are completely correct: you will never use 5Gbps. You won't even use 1Gbps. But the upgrade to fiber will probably make your internet experience feel a lot faster, due to lower latency.