... Now that I'm actually forcing myself to use amphibious vehicles (and take extra steps to inhibit a certain truck-related glitch that makes them impractical...), I double support this. Amphibious trucks are great, but they look a bit silly driving on the ocean's surface as if it were bumpy but solid land.
And a proper dredging ship probably wouldn't have the "only 5 tiles deep" restriction that the amphibious excavators have, would they? That'd allow you to use dredging to get at this bauxite (and other, similarly-placed resources) rather than having to build a massive island around the island, then crater it to reach:

On the other hand, the whole "Amphibious" argument does have weight, since its primary purpose was to enable over-water bridge construction. But that could use a barge, pretty sure real bridges do that kind of thing, and for creating an LZ on another island, that's what you get a landing ship/"ferry" for, to ferry non-amphibious vehicles to some other land to do work. I could absolutely see the current amphibious models being used for "all-terrain" vehicles that could handle boarding (and disembarking from) ferries without a proper terminal, and may or may not also be able to handle steeper/rougher terrain than other vehicles. If you want to cut a ramp into a rock face from the ocean, the excavators might just have to work directly from the ferry boarding ramp, without actually disembarking.
That ferry would tend to have a depth requirement, which could be met by dredging just offshore beforehand.