I'm not entirely sure if anyone really cares, but how long you know someone in an adventuring group has little to do with anything. We supposedly knew Uskton Slek since the beginning, but he turned out to be insane.
I disagree. I think it does make a difference. If it didn't, why come from a different place at all? Also, it's easy to see insanity with hindsight. It's the case in reality, so I don't see a problem with people thinking he was normal until he finally "snapped" (maybe from being covered in blood due to a combat reaction?)
As for the violent ones, only Maelrigar comes close to attacking quite as fast as Vaba did, and even he is significantly more restrained. Remember that Vaba launched a flurry of arrows at a pair of sentient females as a surprise round while Maelrigar was in the group. It wasn't Maelrigar that started that one.
But 90% of Pheron's decision comes from Vaba not being with the group but 4 days before there is this kind of problems. It didn't help his case that he was the only survivor of his "faction" after blood was spilled on deck.
Also not helping his case, In Vaba's backstory he was marooned. I am not sure exactly what is current and what isn't acceptable due to conflicts between them, but I've been operating under the assumption that at some point Vaba has let it slip he lost his last group in Ibaea somehow under negative circumstances. That has colored some of Pheron's decisions.
Even though syrvarris has more playing time, it's the backstory and what has happened so far that has built this situation. Part of the Backstory is the 4 days versus 1+ months.