Honestly I didn't take it particularly seriously at all. Firstly because I don't care about tier lists derived from anything other than usage statistics as they are subjective and opinionated. Secondly because the position of the move relearner and the nature of the challenges you have to deal with in XY are different to the situation in Reborn. This changes the context and therefore a tier list designed for XY has limited application here.
I said as good not just good. You're right, plenty of pokemon have good dual stabs available by level up. The only one's I could think of with dual 120's though? Blaziken, Infernape, and Heracross.
No.
You did not just say that.
The positioning of Heracross is of minor consideration when considering it's worth. Get that thing Megahorn, Close Combat and Moxie and it'll make a huge impact on every single gym after you get it. For me it swept Luna's entire team, it swept half of Samson's team and it made a huge hole in Radomus' team. It is literally vying with Escavalier for the position of the best obtainable late game pokemon period for me right now. Oh and guess what? There's a whole ton of content still to come. You know what Heracross will be busy doing in that content? That's right, the answer's wrecking face.
Or if you're like me and don't use any in game healing items because they make the game too easy.