YMMV - But here is my Verdict on Focus Fire with Abyss Defiant
Mission: Seige of the Warmind (Daily w/Angry)
LV32 with 331 Abyss Defiant -- LV30 Wizard Majors
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With Focus Fire enabled, I was able to take out Wizards with a single clip. Mid-long range worked best and a 70% or so Pricision Shot rate was all I needed to down one of the enemies.
However with Hip Fire enabled, I almost always had to reload a clip whether this was mid-long or close range. This has not much to do with how often I hit a Precision Shot, the damage output is just significantly lower per clip.
Here are some quick stats I whipped up, basically I kept killing Wizards switching between the two:
Out of 20 Wizards, average TTK with Focused Fire was 4.9 seconds
Out of 20 Wizards, average TTK without it was 6.7 seconds
This means, if you are up against a single Hive Wizard Major, you should use Focused Fire because it stops you from needing to reload in between.
Now.
At the end of Seige of the Warming, there is an Ogre. Killing this dude with either takes about 7-8 reloads.
I will upload a video displaying this once it allows me to share it, but essentially this means with Focused Fire, this Orge takes
a much longer time to kill. Case in point, if the Wizards had a bit more health, without Focused Fire they would have died by the time with Focused Fire started reloading it's second clip.
Now I did this over and over and the fact that I tested this on a Hive Wizard Major gives the Focused Fire the only edge it will ever have. It is one of the very few instances in the game where with vs. without kills an enemy in a single clip instead of two.
By the time any enemy has enough health such as that the Abyss Defiant needs to reload even a single time, it will kill enemies faster. If you want to test this yourself, see how much faster it is at killing the LV33 Hive Knights at the start of the Crota fight on Hard.
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What about enemies who die in a single clip for both?
Enemies that range from dying in two hits all the way to 31 bullets will ALWAYS die faster without Focused Fire -- obviously, as there is a faster rate of fire -- 67% faster in fact.
There is a misconception at the moment that Focused Fire allows you to hit precision shots more, and this means it is better at killing enemies. This is not the case. The spread at mid-long range with and without are very similar. But in order for Focused Fire to have similar damage overall for you, is if you are shooting approx. 20% more precision shots because of Focused Fire. (I did a small calculation that takes a lot in assumption and is far from accurate, but bare with me here)...
This isn't a pracitcal advantage unless your ability to hit precision shots is about say, less than half the time as it is. Of course this depends on the person and whether or not they have good control of the recoil on the Abyss, but let's remind ourselves of the sort of distance we will opt to use the Abyss over a Sniper anyway.
Mid-long to short range. Both ranges that is easy to get about a 70% Precision Shot rate without Focused Fire. The only way to do almost equal damage if it somehow Focused Fire is giving you a near 100% precision rate. If there is an enemy in the game that is giving you this, and dies in a single clip too, then why on earth would you be using the Abyss Defiant over a Handcannon or something with Firefly?
You wouldn't.
The Abyss Defiant is used as a Solar Weapon, which of course does not compare to the Vex, but if you go into the Nightfall as it has Solar Burn running, I want you find any enemy that dies in one slip with Focused Fire and not without. There aren't any.
But then it sounds like I am suggesting you should use Focused Fire only on Hive Wizard Majors in Seige of the Warmind right?
Nope. Because you are not only figthting a single Wizard. You will be reloading after killing one, onto the next Thrall or Knght as you continue the fight.
There is never an level in the game that is won by killing a single enemy wins it anyway. So if you went only Abyss Defiant on any stage, you will always shoot more and have more DPS as you will be reloading more than once throughout the stage.
tl;dr: next time you use Focused Fire, just remember that the second time you reload you have essentially halved your protential damage (providing you do have much better accuracy with it).