Agreed for the most part! Let's ban accuracy reduction moves. However, you forgot one item: Lax Incense. As for drawing the line, I think that we should only ban moves that have a 100% chance to lower accuracy (ie Mud Slap, Kinesis, Flash). Banning moves that have a, say, 30% chance to lower accuracy only restricts teambuilding. I do get Octazooka and Leaf Tornado, though as they're strictly outclassed except in the manner of having a 50% chance to lower accuracy. But Muddy Water, Night Daze and Mud Bomb? No. The odds of them actually landing, lowering accuracy, and then causing the opponent to miss is literally the same chance as landing a critical hit.Why Accuracy-Reducing Moves Should Be Banned1. Why we should put off discussion of Deoxys-Defense in order to ban accuracy-reducing moves
If this is going to be a reason that Deoxys-Defense gets banned, then accuracy-reducing moves need to finally be banned. If Aegislash is a winning match-up for Deoxys-Defense because of Mud Slap, Mud Slap must go. The only reason accuracy-reducing moves haven't been banned is because they have been irrelevant, and so have been ignored. Clearly, they are no longer irrelevant and must be banned.
2. Evasion-boosting and accuracy-reducing moves are essentially the same in 1v1
In 1v1, there is no real difference between evasion and accuracy, as there is no switching. Evasion moves are already banned, so accuracy-reducing moves should join them.
3. These moves, abilities, and items should be banned
3a. A note in the interest of uniformity
Now, I don't really think all of these moves are useful in 1v1. If your Octazooka Sableye is not usable if we decide to ban accuracy-reducing moves, then that's a shame. Only Mud-Slap and Flash are problems in 1v1. I think we should ban all evasion-boosting and accuracy-reducing moves in the name of consistency, however.
3b. A note on drawing the line
Looking at the list of every move that increases evasion or reduces accuracy, one might wonder, why ban every move? Why not just ban the problem moves, namely Flash and Mud-Slap and leave Muddy Water for some crazy build in the future. I would argue against this line of thinking because it then becomes difficult to decide where to draw the line at what is too haxy and what is not. Is Muddy Water the line? Is Brightpowder? Is Kinesis? What is the right amount of hax? I would rather avoid having a discussion that will, frankly, be pointless. Who cares if 1v1 bans Octazooka? Just ban everything and be done with it.
Accuracy-reducing moves should've been banned from the beginning of 1v1. They have been allowed to remain in 1v1 simply because they have been overlooked. I have always believed that the moment accuracy-reducing moves became relevant in 1v1, they would be judged uncompetitive and swiftly banned. I believe that has happened in Macemaster's post. Mud-Slap has moved from a harmless meme to a detrimental move. I think the subject of accuracy-reducing moves must be addressed before we can appropriately assess how broken Deoxys-Defense is in a meta without accuracy-reducing moves.
Non-Mud Slap Deoxys-D loses to Aegislash because crits exist.In regards to the notion that Aegislash is a Deoxys-Defense counter:
252+ SpA Aegislash-Blade Never-Ending Nightmare (160 BP) vs. +2 252 HP / 0 SpD Deoxys-Defense: 212-252 (69.7 - 82.8%) -- guaranteed 2HKO
0 Atk Aegislash-Blade Shadow Sneak vs. +1 252 HP / 0 Def Deoxys-Defense: 56-68 (18.4 - 22.3%) -- possible 6HKO
It takes just a pinch of investment to make this unlikely 2hko turn into a guaranteed 3hko. Physically offensive Aegislash may have a chance, but then that risks falling to the popular Iron Defense set, while Metal Sound just makes it into yet another Taunt/No Taunt 50/50.
An important thing people need to keep in mind is that Deoxys has a severe advantage against slower offensive mons, being able to take the win back even after choosing poorly at team preview with similar 50/50's that it uses to beat Gyarados, Buzzwole, Heracross, and more.
252+ SpA Aegislash-Blade Shadow Ball vs. 252 HP / 148 SpD Deoxys-Defense on a critical hit: 288-342 (94.7 - 112.5%) -- 68.8% chance to OHKO
Aegislash gets to use Shadow Ball 12 times before running out of PP. 0.9375^12=0.4610 AKA, Aegislash will get a crit Shadow Ball againt Deoxys 54% of the time. That's where Mud Slap comes in, which drastically reduces these odds because most of Aegislash's Shadow Balls will now be misses.