Doryani's Catalyst + Beacon of Ruin

Hi guys Im new here and in the game. This is my first character so Im trying to learn the game still.

I have a level 70 CI/Flameblast/Vaal RF&Vaal Discipline build ele witch. My question is about Doryani's catalayst and beacon of ruin. I have already give my skill points to Beacon of ruins. Should I buy Doryani's catalyst ? I know that doryani+flameblast is strong duo but doesnt beacon of ruin do the exact combo with flameblast ? What I am missing here ?