Its not just reducing the versatility.
If you want to help a healer or dps, use TBN, giving them a 10% won't be that big of a deal. I also did Dragonsong ultimate and honestly, in which scenario would you give a dps / healer a 10% mit instead of a 25% shield?
The reason for merging those cooldowns is just to be able to add another ability that focuses on DRK's weaknesses: sustain and HP recovery. Otherwise you are basically already double weaving for like 10 GCDs in your burst, now you got to weave 4 defenses to mitigate?
Using Oblation for auto attacks is kind of pointless, you need a better tool to deal with that. Dark Mind's purpose is to work against either raidwides or magical tank busters. Giving this to someone else is over powered? How about Nascent Flash healing you for 1600 potency with high possibility of crit heals and a ~18% damage reduction and a 400 potency shield? Oh never mind the 29% magic mitigation for 10 seconds is ridiculous.