After extensive play-knowledge and observation, the council agrees on 3 vital points: getting a Speed Boost is trivial (with Protect), getting a Swords Dance is not as trivial but still highly probable, and Blaziken can either sweep a significant portion of the metagame late-game with just a Speed Boost or sweep a significant portion of the metagame at any point in a battle with a Speed Boost and Swords Dance.
The first point hopefully doesn't require too much explanation; simply bring Blaziken in, and choose to either Protect, Substitute, or simply KO various popularly used Pokemon, such as Aegislash, Scizor, Tyranitar, or Ferrothorn.
The second point is more obvious when looking at the current metagame. Aegislash does not OHKO Blaziken, so even if you guess wrong, you still have +1 Speed and +2 Attack. Tyranitar, Scizor, and Ferrothorn are near certain switch-outs in most cases, so that is a strong Swords Dance opportunity. Greninja is faster, but after a Protect, Blaziken is faster, which introduces another opportunity to either KO or Swords Dance. This point is actually important as well. After a Protect boosting Blaziken's Speed, many popular threats that formerly scared it, such as Greninja or Gengar, are now OHKOed, which introduces more chances to safely use Swords Dance. After viewing and playing battles ourselves and confirming with the usage statistics, we determined that, while it wasn't as easy as the free +1 Speed boost, it still was not too difficult to get a Swords Dance in to get +2 Attack with Blaziken.
With those two points in mind (that getting at least a single Speed Boost is trivial and at least a single Swords Dance is usually not an issue) it's clear that it's nearly impossible to stop a +2 Attack and +1 Speed, 339 Attack and 284 Speed, and STAB on both Flare Blitz and High Jump Kick Pokemon from sweeping the majority of the metagame. Blaziken has very niche counters (Slowbro is the closest thing to a counter and, even then, it falls to mixed Blaziken variants) and most of the time players must choose to sacrifice one of their Pokémon in order to bring in their revenge killer (Talonflame/Azumarill are omnipresent in today's metagame even because of Blaziken) and force Blaziken out. For the above reasons, the council determined that it would require enormous over-preparation to deal with Blaziken, so meeting that requirement hinders team building and provides an overall negative presence in the metagame.
Though the council doesn't use previous generation comparisons (at all) in determining a Pokemon's status, it might help to view it in a similar context. Blaziken was banned in Gen 5, and Gen 6 has nerfed potential checks like infinite rain via Drizzle, introduced Pokemon weak to Blaziken, such as Aegislash and Klefki, that are popularly used, and given Blaziken newer tools, such as Mega Evolution and the ability to Baton Pass boosts. The latter tool is particularly significant, as it introduces a whole new archetype of threat to prepare for (Baton Pass) that is often dealt with in a completely different manner than the standard methods to check Blaziken. New checks like Talonflame and Azumarill are certainly viable checks, but we felt that these checks, along with the ones that already existed, like High Jump Kick mindgames and recoil, were not enough to trump the ability to get Speed and Attack boosts relatively easily and subsequently (mindlessly) sweep a majority of the metagame.