If you don't want to read my explanations you can skip to the part below the line. I think if you're asking for Soulbeast to be nerfed however, reading it all may help to inspire some thoughts.
I think everyone can agree that Soulbeast is capable of doing a colossal amount of damage in a very short frame of time, often while having a significant range advantage. But what no one seems to agree on is what needs to be nerfed. It's always just a demand for Soulbeast in general to be nerfed.
So for the sake of discussion and education, I'd like to explain why I think ANet has allowed it to exist as it has for so long.
Support builds in WvW are equally as broken as many of the roaming and burst builds. Just because they don't do damage doesn't mean they aren't OP. Many times I've personally witnessed Firebrands literally taking up to a minute to die while 10+ players are attacking them (and for clarity, I don't mean just standing there and dancing in circles, but rather trying to escape from a group). Unless you're fully spec'd in to damage, many of the support/bunker builds like Firebrand, Scrapper, Chronomancer, etc. will be impossible to kill in a 1v1 or even Xv1.
With that said however, WvW is a team game. Although roaming is an aspect of WvW (and an important one), balance in that area is incredibly difficult to achieve. No matter what you do to roaming builds, it is likely to effect zergs as well. And historically, ANet has shown that they will allow roaming builds to exist as they are until they're strong enough to effect a larger scale. As a roamer, longbow Soulbeast is a +1 like a Thief that's most effective at adding to a fight when a player(s) has used multiple cooldowns. In zergs, it can fulfill a role as a sniper, but it is pretty clear how ineffective that is the majority of the time. It can work, but it requires a great deal of co-ordination and often multiple longbow Soulbeasts working together to bring their targets down. Therefore it does not effect the large scale.
"Sic 'Em!" increases pet damage by 40% and when merged, has the same effect on the Soulbeast. 40% is an absolutely enormous damage increase for a single button push. It is a build defining skill for longbow Soulbeasts and contributes significantly to it's burst potential. However, it does not effect core Ranger or Druid, only Soulbeast. Therefore, I believe the most appropriate way to reduce the lethality of Soulbeast without effecting Ranger or Druid, and without making Soulbeast ineffective as a specialization, is to do the following;
Reduce the percentage increase to either 10 or 15%, or do not allow "Sic 'Em!" to effect the Soulbeast while merged at all. Soulbeast, and Ranger in general, still have many damage modifiers and will still be capable snipers without this skill. It will also promote some diversity in that it will allow players who want to snipe to choose Soulbeast and players who want to play Longbow but want to 1v1 to choose core Ranger.
[JEEP] [IH] [HUNT] | Necromancer | Maguuma | Diamond Legend
You've got those dangerous eyes ... ♫