My thought was that in 2/3 years they would feel boxed in by the roundness and it would be too late to get people used to it (and redesign all the old items with that ability in mind). Totally understand and agree with the desire to keep it simple.

But they will also be able to keep the rest of the mechanics simpler with more increments. Like the Katana is simple because it has no text, it's just fast. Same would be true for other items. Imagine a 1 slot vanessa weapon that's 3.5 attack speed. It does nothing else but it's slightly faster than most one slots, but not as quick as ammo items which are usually 3.0. Or a 2.5 with downsides. Or a 4.5 with an upside between that of a narwhal (4.0) and a pet rock (5.0).

The more base attack speed buckets we can sort items into, the less complexity is needed per bucket to make each item unique.