Consumer SSD drives only go up to around 500Mbps, and it's far less for SD card storage. So you won't be even able to download a file with 690.47Mbps! (To stream a video in HD, you only need about 5Mbps).
https://www.microcenter.com/product/600420/inland-premium-51...
That said, almost all phones are not using such an interface or controller for their storage and I do largely agree having a phone with a >1Gbps link is a bit overkill for a handheld mobile devices. Ultimately though once there's a bunch of clients on it your actual throughput in practice will be much slower. The big win is that the overall channel (or channel grouping) can now handle a ton more aggregate throughput meaning higher realized speeds per customer for the same amount of spectrum. Being able to get your slice of data faster means you can quit talking or quit listening sooner and someone else can talk or hear something they care about.
Also, good point about why speed is important - it can certainly help serve more customers!