This hardly moves the needle at all.
Why? What is not mentioned is that Earth has only 0.02% water by mass. The blue marble notwithstanding. Doubling that by doubling the mass of mantel water, gets us up to 0.04%. Most putative water worlds discovered so far have water by mass percentages in the range of 10-30%. If half is embedded in rock, that still leaves massive high pressure ice layers. Earth would have exotic ice sea floor if it had 20-30x more water. That would still be "only" 1%-2% water by mass.
A high pressure ice layer multiple(or hundreds) km thick will drastically encumber the potential oceanic nutrient content. Let alone the development of life. Such a layer is easily attained at multiples of Earth's water content which is still little in the context of most water worlds.
Earth is more like Mars hydrologically. Luckily. Earth sits on a hydrological knife edge. It has a precious mix of land and ocean and sea bed liquid water/rock interface. There is a wide range of posibilities that are either too dry or too wet to be habitable. 0.02% sounds almost dry. But it's what gets us the Goldy Locks state we live in.
