[quote=@Joshua Tamashii]
*Possible Spoiler Warning*

Before anyone complains about War, Devil-Slayer have been show to be able to control the attacks of another mages, as long as those attacks are of the same element. Also, Silver was shown to be borderline immune to all Ice-based attacks. Grey only beat him after having a metal ball in one of his attacks, though the ice still did nothing, while the ball did all the work.

Also, may I point out that this is the magic that gave a guy the ability to freeze fire? And the ice was immune to Natsu's flames.

EDIT: Albeit, I'm using Fire but still, you get the point I'm try to make.
[/quote]

Where were they shown to control other Mages' spells? I remember Silver being immune, but all slayers are immune to non-slayer elements save for special cases like that time eating different colored flames made Natsu sick because of the taste. If Gray had fought an Ice Dragon or Ice God Slayer they'd have done the same thing, just eating or withstanding his ice.

Those other two points don't point to a specific trait of the magic itself, but Silver's strength as a mage. Silver was also alive in the first place because of another point, and for all we know his power could have been boosted by that. If it was Gildarts with Fire Dragon Slayer magic instead of Natsu, I'm betting he'd be able to do similar feats. 

Just because it shows up later in the manga, I don't think that puts Devil Slaying immediately above the other Slayer types. In fact it actually seems weaker on the whole because of the enemy they were fighting at the time:

Dragon Slayer magic was made to fight Dragons. When Dragons actually showed up, no one but the Slayers could even hurt them--and even the slayers couldn't completely defeat them. This is a case of the Dragons being outright invincible save to one thing, but just having that thing doesn't mean they die, it just means that you can now inflict damage to them. If your strength isn't on par with theirs, having the Slayer magic won't help.

Devil Slayer magic, on the other hand, was made to fight the Etherious. And those demons were being defeated by non-Devil Slayers to begin with. In this case, it's more like Kryptonite and Superman--if you're strong enough, you can beat him without Kryptonite. Having Kryptonite just makes it easier. Or like Pokemon type advantages. A Devil Slayer is super effective, but a normal mage who's outright strong enough can still beat the demon. That says, to me, (along with later events where things regarding dragons happen and the reactions the demons show to them) that Devils are lesser than Dragons. 

And it's already been seen that, unless the Dragon Slayer uses a special method or has much stronger base stats, so to speak, that God Slayer magic is inherently superior.

Not to start a huge fight or anything, that's just my stance on it.