a shackleton flying two dead engines on the same side (for display) apparently quite manageably
That's a case of good energy management - feathering two engines of a four engined aircraft at relatively high speed (i.e. well above Vmca) is a very different thing than feathering an engine from below Vmca, while trying to accelerate to it.
While operating below Vmca the control issue is of primary importance, drag being a secondary challenge if control can be maintained. By definition it cannot, of course, without reducing power or increasing speed.