Have you actually played or run with it in the game? It's a bigger deal than you'd think.
Especially when people start doing ridiculous things like Salve of Power and Secret of Creation along with it.
I've just seen how problematic Close Blast 3 powers are. Against Fort? How many times do Wizards use Thunderwave against more than 1 or 2 foes. The Invoker is lucky to stun 1 target with a Daily. Or the Invoker might be swamped by the foes that he missed if he steps away from group protection to get an opportunity to attack 3 or more foes with it.
Remember, stun is great. But, it just stops two attacks per foe (on average, most foes will save in two rounds), one of which would have missed on average anyway. So each foe stunned turns a single hit into a miss on average, slightly more with area attacks. In an encounter where there are 20 successful hits by foes, stopping 1 to 3 of them (and sometimes 0) is good, but it's not broken. No more than a Daily healing power that heals more damage than would have been taken in 1 to 3 successful attacks is broken. Beacon of Hope is stronger than this in reality. Its strength is just different (heal lots of damage, weaken foes, affect more foes, does not adversely affect allies).
As for Salve of Power and Creation Secret, it's just a matter of synergies. Every time WotC allows powers, items, and feats to allow PCs to not expend some power, there's the opportunity for abuse. But the combo here on average allows the player to use Silent Malediction ~3.2 times per day. It costs an item (which can be used by any class to regain a daily, so no advantage for the Invoker) and 2+ healing surges to get this many stun attempts. Invokers are 6+CON healing surge PCs (the lowest in the game). If they use up 2 or 3 surges a day doing this, especialliy with a blast that forces the Invoker to get in close, they are taking a risk and they are reducing the number of encounters per day (on average).
I'm not saying Silent Malediction is bad or average. Like Sleep, it is above par. It's just not broken. It's definitely on the top end.
And Salve of Power can be used by any class for any tweaked out combo, so...
As for Creation Secret, a PC could just go ahead and buy/craft two or three Salves of Power by mid-paragon and have the same advantage as the tricked out Invoker.
People see the word Stun in a power and freak.