Depends on your definition of "overwhelming" 1 in 5 convicts are in prison for drug related offenses[1]. Almost four hundred thousand US citizens behind bars for plant byproduct possession or distribution is heinous. There are around 320k prisoners for property crime, by comparison, so no, nonviolent drug offenses are #2 in terms of incarceration blocks, though the numbers are close, and violent offenses are over twice drug offenses.

[1] http://www.prisonpolicy.org/reports/pie2016.html