Weathering olivine doesn't scale, because you need so much. It involves hitherto unprecendented amounts of quarrying and then transport. The quarrying would destroy massive amounts of habitat. After the waves do their trick, near-shore habitats would be devastated because the entire ocean floor is covered in olivine.
I am a former geophysicist by the way. While I did not work in geoengineering, I am familiar with most of the serious proposals with scientific support. Be skeptical of these groups that claim to have an easy answer. I can tell you that no one in the field thinks carbon capture from the atmosphere is realistic anytime soon. The scale is enormous. Most people have trouble understanding the difference in scale with what we actually have the capability for.
The only problem is that some people pretend that this glimmer is a guaranteed solution.
These kind of pie-in-the-sky things takes money and attention from real solutions that work. They are false hopes that make people complacent and the problem seem less urgent, thinking that we'll tech our way out without fundamental changes to how we live on this planet.