Independant economist: one tenured by an independent university as opposed to being employed by a lobby group or think tank to promote a specific agenda.

When even Adam Smith supports the regulation of capital, this can be considered a fairly mainstream position.

Summarizing Piketty's recommendations as "the regulation of capital" is absurd.

I can point to dozens upon dozens of independent economists (by your definition) that disagree with the use of confiscatory income tax rates and wealth taxes, so I don't know what your argument is here.