Depends on the weapon obviously,but how many Defense Ups do you REALLY need to make this ability ...

[CM2]

work?

I've seen 1 main/3 subs or something like 2 main/2 subs or even crazier like 2 main/6 subs.

So my point is when enough is enough?

 

[mysticcalm]

I think there's a maximum and the power ups don't stack like how some people think they do. I can't remember the percentages off the top of my head but I know that a main defense up increases defense by 5% and the smaller ones do something like 2-3% and then the more smaller defense ups you have then the percent gets smaller for each one. Squidkids made a video about this

You can watch it here :

To answer your question I think there needs to be some testing. Just watch the video and you'll learn more about how useful they are and when they start to get unnecessary since the percent gets too small to make a difference in my opinion.

 

[Lester Roquefort]

I think it's over 4. I have 4 's and it's fun as hell to play Rainmaker with em.
Incidentally, i'm a good Rainmaker carrier. Every inch counts, you know... and by good, i mean, i just nab it and run... i really need to start shooting with it.

 

[NotAPerso]

work?
I've seen 1 main/3 subs or something like 2 main/2 subs or even crazier like 2 main/6 subs.
So my point is when enough is enough?

I run 2main/7sub of defense up (along with 2 subs of ink saver [main] and ink resistance) while using my .96 Gal Deco. I laugh off uncharged charger shots and burst bombs and roller flicks, and I'm able to power through .52 Gal and Tentatek shots so I more often win rather than trade or lose.
I don't think any more defense would be of great benefit but a little less can still be effective.
Personally I think the absolute minimum of defense to be effective is 9 subs (or relative equivalent) because you still survive uncharged charger shots and burst bombs and those are very important things to survive but you're not likely to take an extra hit from. 52 Gal or Tentatek with that amount of defense.
Also playstyle is very important in fully utilizing extra defense. Running into close range still gets you killed so play at a comfortable range and if you've been hit back off to heal before attacking more.