A few inefficiencies I can spot initially from seeing how everything fits up on the spreadsheet.
First, your TD doesn't line up with Trick Attack because you go into DWT later losing the extra 16% dmg it gains. Everything I've read says that dmg buffs are multiplicative rather than static increases, so this makes the 10% from trick attack a lot larger than the 10% it shows. Second, you can fit 3 more GCDs in DWT if you end with ruin 2. You'll be cutting it VERY close if you don't have enough spell speed but I was able to JUST barely do it in 145 gear and 180 gear has made it a lot easier. Third, there is an error in there. Your 3rd fester is impossible so I removed it.
Lastly, the entire rotation (taken until your buffed dots wear off, including reapplication of new buffs) is only 146.44336 pps. Very much lower than the DWT rushes. Even with my inaccuracies on them the difference only amounts to like a 5 pps difference from what they should be. (I also used RS as 25% cause for some reason I was convinced it was, and it took a while to fix) If I take it until you end with DF like I do with the others, its only 162.98 pps. If I do the same thing I did with the others, yours comes out even worse. The worst part about it is, you lose a tick of bio at the beginning.
SMN is very hard to get accurate numbers for because of the pets, if someone could let me know how much potency both enkindles are that would seriously help. Also, ifrit is worth about 40 dps more than garuda (195 dps ifrit vs 152 dps garuda) I had them sitting there attacking while I was hitting their abilities in the manner you would in raid for about 3 hours last night. They'll probably do a little bit more in raid but yeah.
Funsies: https://youtu.be/rChZgQODfAE I apologize for the quality, the source video is higher quality but youtube nuked it. :/ This demonstrates the 6 GCD DWT, I hit Deathflare at 2s, and DWT wore off at 1s. I've tried ending with other spells but unless we can knock off 1.6s off 6 gcds I don't think we can. It would take the FCoB levels of SS that BLM had to do this. We could PROBABLY do it during Fey Wind but its still a stretch.
EDIT: With Fey Wind it's possible to finish off DWT with ruin 3 instead of ruin 2, however it's extremely close and I wouldn't suggest doing it unless you know you have good latency or the spell speed to do it.
The benefit of spell speed to GCDs has been reduced to a little over a third because of level 60. At 573 Spell speed I have 2.41 on the GCD, if the numbers were the same proportionately as they were in ARR it would read 2.3 or something. This means somewhere in the upper 700s of spell speed would be required to do Ruin 3 during DWT as an ending spell before Deathflare would be required. Somehow I don't see this being possible until way later.