I wouldnt say you 'need' it. i missed out stamina on my PB and the end drain was massive. i tried slotting Nova and Dwarf with End Reductions but that really is a waste of very valuable slots to a PB/WS (soooo many powers). i added Stamina in and found him far easier to play.
I'd suggest a yes to taking Stamina on your PB.
Just my opinion
It totally depends on your playstyle. IMO a triform doesn't need Stamina unless it's mostly human and running the shields. Mine is triform and I have no need for Stamina whatsoever, but I don't have the shields and never spend extended amounts of time in human form. Light Form has boosted endurance recovery so that's not a problem either. There's also Conserve Power to help with any temporary endurance draught you might have.
Edit: just in case you don't know, passives like Stamina only work in human form.
Also useful to note ... stamina doesn't work in dwarf form 
so for me who mainly uses that now it's pretty pointless.
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Edit: just in case you don't know, passives like Stamina only work in human form.
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Doh! knew i forgot to mention something 
If your pb is human build only like mine then yes take stamina, even with it i still find my end runs down faster than with any other AT i play
Had stamina but dropped it to let me pick up more powers. I use Conserve and with Hasten it can be up 2/3 of the time. When it's not up then yeah, you can have real problems, even with end red slotted on all the attacks. On the other hand when you hit hasten and conserve energy, you can lay some serious damage out in human form with no end problems. 
I'm also tri form so can switch if I get low during the times conserve energy is not on too. A more erratic style but I found it more fun. Thing is, currently someone is usually buffing with RA or something all the time in the teams I get so I never even need conserve running.
Don't slot Dwarf for end reduction!
The forms have stamina built in so slot them for End Recovery!
I can fight in human form, then when the end runs low, whack on Conserve power and switch to another form. Bingo. Instant Stamina. Just make sure you've got conserve three slotted with Recharge.
Okay it means I gotta keep switching forms, but thats half the fun of PB right?
It's worth it to save the three power slots it'd take to get Stamina.
I'd say it's worth the three useful power slots to get stamina to avoid being confined to the forms for endurance recovery.
I hadnt even thought about stamina or had endurance issues and then suddenly i was able to pick conserve energy. Human form builds id say yeah get it, but i tri-form and find it works great. I have no doubts ill be able to have a pure peacebringer at 50.
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
If you are tri-form stamina is not essential. If you are going to be spending most of your time in human form stamina will be basically essential. That is just my experience from playing my peacebringer to 34, having tried tri-form and a human/dwarf build.
Prior to ED I toyed with a build on the test server with perma-hasten plus conserve energy six-slotted for recharge, with no stamina. It was just about viable but ED put paid to that idea.
Yes, I know the argument that no-one 'needs' stamina, but my Blaster, Scrapper and Corruptor all got so much more pleasant to play after I picked it up...
)
So, how about Peacebringers? Mine's just hit 14 and doesn't really seem to have end problems yet, but I know if I want it around 20 I should start planning now (not at 20 of course, that'll be for Dwarf form
At the moment I'm planning to go tri-form if that makes any difference, 'cause shape-shifting's cool and none of the other AT's can do it