I'm guessing you meant
[Idol of Terror], not
[Idol of Ferocity]. And if you saw a 200dps loss between Terror and Everbloom, you were doing something massively wrong, or weren't getting the same raid/group buffs/debuffs. Neither idol comes even remotely close to providing 200dps on their own; you could go with no idol and not see even close to a 200dps loss.
And regarding the comparison... 58% uptime sounds about right, so that's an average of 38 agi constantly... It never applies to Rip or mangle, but does apply to Shreds and white attacks. So you could estimate it at about 45agi to white attacks and shreds. So like 50ish AP and 2%crit to shreds and white, or 120dmg per shred. That means like 90dmg per cycle vs 250dmg per cycle... Everbloom wins, by alot. (Note please that those are very very ballpark figures, use Rawr to find accurate figures for you. But I don't expect there's any way Terror could beat Everbloom.)