General

@lolitstom: Theres far more sources of boss+TD making scale lower faster. Have not tested it out yet but yes of course att% eventually gives diminishing returns but at a much slower rate in comparison to boss%

@ieatrice08: the notion that % atk does not suffer from diminishing returns is false. It suffers just as much from diminishing returns as %boss %td does.

If youre approaching super end game. The balancing point is actually closer to 450% (boss +TD) and around 90% atk.

And absolute perfection is actually to have 5 lines of %atk and 1 line of ignore defence on emblem would result in all primary potential lines of weapon and secondary to be boss lines and all bonus potential lines be %atk lines. These numbers already factor in hyper stats, nebulites, link skills and typical class %damage boosts (most which sit around 50%)

It can be argued that two lines of Ignore defence would result in better gains on some bosses though.

@klytta: You have a good point honestly. My emblem contains mostly just PDR so I definitely do not have too much %att on my DB. Was not very clear in my statements but I was referring to only main pots. If talking about bonus pots then yes it is definitely better to go 2L% boss. DBs also utilize more final damage than total damage so the do gain a lot from boss%. I read somewhere,however, that the ideal amount is 250% since the gains start to decrease (for example 0-100% is an increase of 2x regular damage but from 100-200% its a 1.5x increase in damage and the gains diminish the higher up you get also boss% is additive to total damage which you get from hyper stats and link skills). I put in 230% as the ideal amount to match 250% boss since DBs get blade clone for 10% total damage and 10% for the other hyper skill buff (230+10+10 = 250). However DBs can gain tons of boss% due to the SW katara giving an innate 30% boss so you have a strong point in the ease of reaching 350% boss. I will definitely try them both out but I just wanted to explain the theory in why I currently greatly prioritize att% over reaching the standard boss% lines on each weapon. I second main a phantom and for my phantom the %boss scales well with them due to them also utilizing little total damage and more final damage so I can see where you are coming from.

my emblem is 35% PDR and 18% att so emblem is done
i will follow what you have and aim for %att katara with 2L %boss on dagger

@ieatrice08: All I'm going to say is that end game wise you're shooting yourself in the foot. And going pure %attack isn't the best strategy at all. While the loss of 52% boss for what ever amount of % attack you gained was helpful for you. It was most likely due to the fact you were already % attack deficient. You can hit 350% boss with 80-90% attack if you aim to reach perfect gear. If you instead go pure % attack you will most definitely lose out on damage. That being said a good God tier set up is to have double boss on a Fafnir dagger and %attack on a SW katara. Look at my old screens to see what I mean.

DB scale very very very well with ATT % (due to double weapons). Go full all out att% and replace all boss% lines with it while throwing in two 20% boss nebs. This should result in 230% boss (including linkskills and hyper stats). Even if it is less, the gains from ATT % greatly outweigh Boss% (I tested both damage outputs and att% was significantly better even though boss% dropped from 225% to 178%). Boss% is honestly overrated since it is additive to damage% and is honestly only really good for classes that do not have much total damage% or base weapon attack (like phantom or wild hunter)

Neb's should always be 25%boss over 4% attack. Perfect set up would be 2 boss lines 1 attack line for main potentials. Then 2 or 3 %attack lines for Bonus Potentials. However, due to cost of bonus cubing a %att top line with a %boss/%damage/%luk line is fine. For emblem you'd want 21%attack with a 35-40% pdr line (main pot) and same bonus potential as said above. End game wise you'd be looking at roughly 340% boss or more.

Now all of that being said. Should you get 21% attack or 30%attack main potential absolutely keep it.
Oh I need to mention. Your visible %Boss and your actual can differ. As a DB we get %pdr on skills so for %boss it's not really an issue. But for our PDR calculations you need to factor in PB's added %PDR. In simple terms, if you have 87-88% visible PDR you'll have 92-93% actual when using PB. Which is the lowest I'd recommend for doing bosses like vellum. A good place to stop is when you have 90-92% visible PDR.

Cube your weapon that has the least %boss/%attack mix and try to get 2 lines of each to start. 2 boss lines will better suit you due to bonus potential being a easy extra line of %att. If you do not have an emblem at all start with that, aim for 2 lines of %attack or 1 line %attack + 1 line %pdr.