How heavy can IRS penalties be?

When the IRS billed the Estate of Michael Jackson for $700 million, $200 million (28.6%) was an underpayment penalty.

(P.S. the IRS lost an appeal on the tax bill, and will have to reduce the bill and eliminate the penalty, but only after the estate paid thousands in attorney fees to contest the tax bill. The tax dispute dragged on from 2010-2021.)