Imo, you need actinics, wether you have high-light intensity corals or low-light intensity corals.
The reason is simple, In the Ocean there's no actinics. just Sun light. which in our enclosed system we try to mimic with mh's..
Now imagine if the Sun just came out (at full spectrum)all of the sudden without any daylight in the morning, and at night Sun goes away without lunar ligh, into peach black. you guys ever seen an Eclipse?
We cannot lower/raise the Mhs intensity throughout the day . just like the sun rises from its lowest to its highest point....
once we turn mh's on, they stay on at the highest intensity spectrum untill going off. So you need the supplements of lesser lights (preferably flourecents/actinics) to regulate photosysntesis .
Every life organisms needs a specific lighting intensities/spectrums to regulate their life processes, even though mh's are white in spectrum, they're composed of a broad band of colors which cover the optic spectrum..
That said, in controlled ecosystems(like our tanks) corals and other organisms respond better to the amount of light received, rather than the spectrum it was delivered..
The reason why low light corals utilize actinics and most of blue spectrum its because thats all they been exposed to or can reach. the reason is : they're deep in the Ocean....
Unlike most corals in reefs which are mostly in really shallow waters...(2-10 feeet). the deeper you go dowm the darker.