There's no way Det is better than SS on Scholar. Det and SS essentially boost DoTs by the same amount, but SS ALSO decreases your GCD.
SS isn't only useful if the fight goes on long enough to fit in an entire GCD, but also helps in scoring the finishing blow.
Even if the fight doesn't go on long enough to add another whole GCD even if the spell speed person is half a GCD faster that means he has a 50% chance of finishing one more broil over the person without spell speed. Over time being able to finish that one last broil 50% more often will increase your damage by 50% of a GCD so even if a fight doesn't go on long enough to fit in an entire extra GCD SS will still statistically increase your DOT
This also applies to moving and escaping from AoEs. The higher your spell speed the higher chance that you'll be able to finish your current cast before you have to move vs someone without spell speed.
When a person with higher spell speed will be able to get off more Broils than the person without Spell speed because the person without SS will either have a higher chance of needing to interrupt his cast or have his last GCD be a Ruin II instead of a Broil because you don't have enough time to start and finish another cast spell speed is going to obliterate Det especially since so much of Scholar's kit is also boosted by spell speed with their large numbers of DoTs.
(And there's a good chance that SS affects DoTs more than DET. The number you linked was for Whms. For Smn Det only affects them by .0001238 [ https://dervyxiv.wordpress.com/damag...er-mechanics/] )
Also you have to keep in mind other things such as the person with the higher Spell Speed will be able to Bane faster which is a pretty big deal especially with DPS happy groups that have the potential to kill a pack of mobs before your DoTs even expire.
