Spot on right there. Haunting looks like its designed to avoid a bigger nerf of increased cool-downs that hits everyone flatly.
High dc casters can probably deal with a longer cool-down, but its the moderate dc caster who will suffer due to a less reliable dc. It becomes that much harder for a new player to play a caster.
The problem is, its not an easy mechanic to understand. There are many suggestions that tries to "mitigate" the haunting mechanic, but are actually a bigger nerf than haunting itself!! Such as much higher saves and SR. People seems to prefer insta-killing at, say, 50% chance all the time, rather than be able to insta-kill at 95% chance some of the time, provided they do it at a reasonable rate. I think there was even one suggestion that proposes limiting wail to 5x per rest.
If a straight up cool-down increase appears more platable, maybe that's the way for Turbine to go...?