Should have used it to prevent Brexit.

Just look at the US right now to see how civil military control can go off the rails too.

I think the monarchy could have used its power to prevent Brexit, but the monarchy never uses its voice for anything controversial for the most part, that there was a valid referendum and the closeness of the vote and rancor at the time from leavers who held all the reins of power at the time might have made the partial public funding of monarchy untenable, too. Queen Elizabeth seemed particularly neutral even on Brexit, maybe Charles would have done differently?