Droop governing is characteristic of most turboshafts pre-1970. It's relatively easy to implement with hydromechanical controls of that era, and has the advantage of giving a fairly crude means of load sharing in multi-engine choppers.
A few engines had "droop compensation" - wherein the droop line was mechanically "nudged" through a link to the collective stick. (Pull more collective, and the droop line is repositioned to hold constant rpm.) GE's T64 in the H-53 series is an example.
For true isochronous governing, electronic controls (either analogue or FADEC) have been the only practical solution.
Transient droop can also be largely overcome with electronics - the black box senses the rate of collective movement, and applies power to attempt to "get ahead of" the load demand.