SCT can be installed alone. SCTD must have SCT to be installed.
I had errors when I tried to use SCT with SCTD being not loaded.
Blizz damages were hidden as well on the mobs as well, and even by re-enabling them on the interface menu, it got disabled right after.
Every change I tried to make in SCT got me an error (don't have the details in mind).
After loading SCTD and disabling it, it went back to normal.