I agree with every word you said. You will probably need it only for 1% of the time.
But you see, 100Mbps Internet connection dont often give you 100Mbps connection all the time, if gives you a share of total connection, whether that is building, floor, flat, etc that guarantees under X condition you get 100Mbps. So in reality you really want this number to be at least 10X because the system was designed to be oversubscribed. ( And it is not the fault of any body, the tech was designed as such. ) And it is especially true for DOCSIS 4.0.
And in the case of Network planning, it will actually be better if they could speed up your 1% need so you leave more time and space for others. ( Of course some people abuse the network but that is a different story )