It's probably lag. I've had it instantly (relatively speaking) save me from Mountain Buster, and other times not so much for instance.
Besides, the sequence can be preemptively compensated for in most cases.
Every instant ability that's off the GCD should be truly instant. I hate how everything has some lengthy animation that takes 0.5 to 1 second to fire, and in that time you can't even use anything else.
Scholar seems to have shorter cast animations and effects than most classes, I find. I can quickly follow up most spells with an instant, and even fit in 2 spells per GCD easily.
Aero and Regen are far more responsive when it comes to "instant cast" than Benediction. Using swiftcast makes Bene the kind of instant cast it should have been. It's really due to the animation you do before the spell is cast. Can't speak about Hollowed Ground or Holmgang, but I'm assuming it's for the same reasons.
That's what I was thinking, because it seems like I have much more success saving a tank from a really bad situation by mashing Lustrate, compared to Benediction.
And considering we get one Benediction every 5 minutes and 3 Lustrates* every 1 minute, I strongly suggest making Benediction instant.
Holmgang is also the WAR's Tempered Will. It's useless for the Oh Shit moment when you are about to get Landslided off by Titan EX or his adds because by the time it's done animating you are already flying off the arena. So useless. You might as well not have it. The best part is when you see it go on cooldown as you are falling, that's just pure spite.
Will they fix it? Who knows!
As a WHM, my Benediction is mostly used to save someone dying (usually DPS) when I'm busy keeping someone else up and can't waste a cure cooldown on anyone else.
Seldom necessary to use it on tanks.
I don't consider it an "oh sh*t" ability.
Lustrate on SCH however is quite useful as an "oh sh*t" ability, but it also only recovers 25% of a targets max hp in one hit.
Take the time to go play other MMO's and learn how most instant cast CD's work and come back to this thread with actual experience. This is poor design on SE's part and it's awful that they can't understand what the word instant actually means. To add to that they seemly have no idea what "off the gcd" means either.