Spell Speed in 3.x was the most powerful DPS stat for SCH, but did not benefit healing much because it did not affect embrace or OGCDS. With the removal of Bio and Aero, DoTs that could double dip the effects of Spell Speed have been made less important, shifting DPS to being mostly about broil uptime.

Crit is once again king and DH as a secondary option for a flat DPS increase. Going det isn't necessarily a terrible option. Melding full DH on a set might give you a 6% DPS increase, but melding full Det would give you a 5% increase with an increase on healing. Most of your slots will be filled though by crit, so either side is honestly negligible.