Seraph is stronger than AST's LB, dude. She puts out an enormous amount of healing over her duration and the CC shield is exceptionally strong. It's pretty funny watching your team shrug off WHM and DRG LB at the same time. AST's LB is only stronger if you can somehow get both your team *and* their team in the AOE, but it has a long cast time and the AOE isn't large enough that the AST can accomplish that without putting themselves in the middle of a fight.
Also worth noting that Seraph is 90 sec vs AST's 120 sec.
There is nothing wrong with SCH, though. People undervalue buffs, shields, and dots, but that's because they aren't willing or able to actually analyze fights and understand what a major impact those things have. They only notice the big bursts and they believe that those are why the kills happened... ignoring the shields that prevented deaths, the dots that lowered enemies into burst range, the damage up that gave them enough damage to secure a kill, the damage down that prevented them from dying to an enemy burst, etc. All of that stuff isn't visible on the score sheet and isn't likely to be noticeable if you aren't paying close attention to your numbers and their numbers. But it's hugely important. Same with healing down - it's not some big flashy number so people undervalue it, but when running out of MP is one of the most common ways to kill someone or force them out of the fight, and healing down makes their Recuperates less effective... it adds up, especially when you add in the damage up your team has, the damage down they have, the dots, etc.
SCH's impact is all very "passive." You setup your buffs and dots and wait for a good opportunity to Mummy the focus target (the first Mummy is often just going to be on a tank if someone doesn't Leeroy in like a moron, since the faster the tank runs out of mana the faster they'll have to leave the fight) and just keep managing your buffs and dots throughout the fight. You don't get any big flashy numbers. Even Seraph is kind of "passive" - you summon her and she throws out a nice buff and then she'll throw out heals periodically but it's not something big and flashy like WHM's laser or SGE's thunderdome.
I mean, your argument against using a Recitation for a teamwide 6k shield is exactly what I'm talking about. That's basically an extra 10% HP for your entire team, a little over that for casters and healers. If you don't recognize the value in reducing your team's incoming damage by *6000*... well, you're just proving that you aren't actually paying attention to numbers and how everything's working together.
It's like oh 10% damage up is only an extra 500 damage on my Broils, big deal. But an extra 500 here or 1500 there is literally the difference between a kill or not in many cases. And therefore, the 4000 or 6000 HP from a shield can be the difference between living or dying.
Giving your team an extra 10% HP and 10% damage up for 15 sec from a single action is *immensely* powerful.