Moody is just that: Inherently broken. Any Pokemon that has Moody, even with the worst possible stats, nature, and even at level 1, could by itself sweep an entire team simply because of the luck and chance the ability provides. No other ability provides that kind of power, so no other ability is therefore broken on it's own merit, and no other abilities should be banned.Almost no ability can possibly be "inherently broken", since almost all abilities can only be of benefit if the Pokemon they're on can be effective. But for some Pokemon, their ability is a fairly minor part of their power. For some, it's more significant. And for a handful, it's one of the biggest factors; the Pokemon would be lacklustre, even outclassed, without it.
This is essentially the dogma that I'm challenging. What tangible benefits does it bring? "Simplicity", but really, banning a Pokemon with a specific ability is hardly complicated. Meanwhile, the drawback is reducing diversity, potentially in UU as well as and more so than OU.
You just said it yourself. Abilities are part of what makes a Pokemon as good as they are.
If we allow people to ban one Pokemon + Ability combo, then what's stopping people from arguing Pokemon down tiers with their lesser ability? Pokemon + Ability combo bans allow this to happen. In the case of Blaziken, we would have Speed Boost Blaziken only allowed in Ubers, and Blaze Blaziken allowed in UU up (or whatever tier Blaze Blaziken would end up in). Now, try making tiers for every single combination of Pokemon + Ability combinations. And who's to say it stops there? People could argue that a level 70 Kyogre is not Uber in comparison to other current threats, and should be allowed to move down to OU, and then level 50 for UU, and so on. Notice I haven't even mentioned Items and Moves yet either, which I assure you would be used to bring Pokemon (i.e. no Dark Void Darkrai) down to standard play. This is why Pokemon are assumed to be at their peak, so you don't end up with a ridiculous amount of restrictions just so that every Pokemon can be used.