Can Someone Explain

[Lyrinn]

I like the DPS aspect of DET , but I dont DPS as much as I should as SCH , mind me asking what endgame content do you truly dps as a SCH. Some of the harder fights 6-9 I might do a bio and misma rotation but thats about it as the tanks are constantly getting cleaved for 3-5k at a time.

DPSing in Coil is wholly dependent on your co-healer. If either you or your WHM are not comfortable with you DPSing, then your windows to do so drastically shrink. With that said, there are plenty of places you can sneak some DoTs in.

T6: All of phase 1 since there's very little damage going out. If your other healer can't handle this phase alone, I don't have anything good to say. Phase 2, you can DoT right before Blighted Bouquet and let your fairy heal people up while it's casting.
T7: Basically any time the adds aren't up.
T8: Pretty much the whole fight if your WHM is competent, just use Rouse + Whispering Dawn (if you have Eos out) on Defensive explosions and Lustrate MT if needed. Adlo on Brainjack/Allagan Field as needed.
T9: You can DPS for most of phase 1. All you have to worry about is Adlo before Ravensbeak. Golem phase you can DPS the whole time. Phase 3 you can DoT after Heavensfall and then Bane onto the add. Phase 4, you can DPS outside of Bahamut's Claws.

Again, all that depends on your co-healer.

Also, your DPS "rotation" primarily consists of Shadowflare, Bio II, Bio, and Ruin (II) spam. You can Miasma if your accuracy is high enough. Neither Bios nor Shadowflare can miss which is why you apply them first.