So I finished Apoc, and dumped astrals and most of my Rostam fund into it (had to do it).
Honestly I don't regret it, the damage is really nice and it becomes insanely hard to die on certain things.
I use 5/5 Ratri+1 with Cata and have a hybrid set with 4/5 Ratri+1 and Sulevia Legs+2 for a huge HP pool/MEVA+. I offset the DT+ with Dring/Vocane/Loricate+1/PDT Cape/Staunch+1/Etc
The Max HP in the weaponskillset/tp set keeps it at around 7-8k HP with Drain 3 DS/NV. (Still working on my Drain 3 Sets)
The buffed Catastrophe seems to be on par with Cross Reaper spam at 1k TP using Anguta/Moonshade. Only it self skillchains and heals you. If there is any tp overflow you can go back to using Cross Reaper as well.
Regarding Calad
There is no doubting it's high damage potential. Great Sword on DRK isn't really my style though. Scythe compliments me very well and makes it very easy to Self Darkness/Fire off a Drain 3 MB. When I use a great sword I feel more reliant on outside support and I actually have to manage my MP more/Hold Back a bit.
I've never been able to really fulltime Souleater on things, I feel like I play a bit too defensively/conservatively. Spamming Cata it's not a problem, and smashing things with close to 8K HP is glorious.
Calad is on my to-do list however. I need to get the proper WSDMG gear for it. I still need to finish relic legs/+3 my AF body/Feed Oseem stones for Ody Head Augs.