Trading off safety and performance in the kernel

That's just the link speed between the storage device and the main system and has little bearing on how fast you can actually write data to disk, especially if the disk is spinning rust. If the disk has to seek between writes then you aren't going to see more than around 100 writes per second which can be just a handful of megabytes, regardless of what the link speed is.

Your examples include a read heavy, write little web server and a db server which is probably explicitly flushing every IO to disk so that there is little data to write back in either case, neither of which is representative of how a laptop is used. It's easy to create a bunch of buffered writes, by copying a DVD image or compiling software or copying memory to disk for suspend, and on a laptop you may delay writes longer than normal to keep the disk subsystem in a low power state for as long as possible, leading to a storm of activity.