Dude, what are you smoking?
A, Brungkeru is far more common, and B, you ripped off Regigigas' title.
And I have no clue what your second paragraph is even talking about...
I think he's attempting to say that the pokemon that are centralising the metagame almost as much as when Garchomp was around in Gen 4, aren't broken, they're just used so much because they're better.
The question is, where do you draw the line between broken and better?
Anyway, on the topic of Terakion, while it's an absolute beast if it sets up, that's the issue. Setting up. Terakion has a cubic buttload of weaknesses, there's very little which it can switch in safe on, or set up safe on, especially in this metagame, which is dominated by Water types, and Ground-types.
Seriously, Terakion is weak to:
Water, Grass, Fighting, Steel, Ground and Psychic. 6 weaknesses, that's almost as bad as Celebi.
Then, bear in mind, what are the most common types of attacks being thrown around right now?
Water, Fighting, and Ground.
Grass is mildly common due to Sun teams and Nattorei [As if Nattorei would stay in on Terakion... but Terakion can't switch in]. Psychic is being used more often, due to the general lack of Steels and Darks in this meta compared to Gen 4. [I'm seeing Psychic types actually use their Psychic STABS! BLASTHEMY!] Bear in mind, said Psychics are Latios and Ranku, which are both somewhat common, and hit very hard with said STABS, more than enough to OHKO Terakion.
But it dosen't stop there, no. Look at what Terakion resists:
Bug, Dark, Rock, Fire, Normal, Poision
6 Resistaces, not bad. Until you realise that the only two of those types which is used even semi-frequently is Fire ad Rock, and even then, with all the Rain and Tyranitar running around, Fire is not *that* common right now. I dare you to find a Poision-type attack in the current metagame, that isn't Toxic/Toxic Spikes.
Terakion is good. Unfortunetly, the metagame... kinda spits at it's Rock/Fighting typing, and makes it difficult for Terakion to actually get in and set up.