My impression is that they would apply more to Janoa than to Brudvir. That's because Brudvir have enough correlation with classic Nordic memes to attract a larger group of players than just PvPers. Wolf-lovers, arctic aficionados, wannabe pteroguin-hunters (or riders), woodworkers, and lumberjacks are among the diverse interests the Brudvir attract. Janoans do not have the advantage of a ready-made set of correlatable memes from popular culture. If their lore is filled out a bit more, the situation for them can become more balanced.
I don't think survival will be an issue for any tribe because, at a minimum, all the tribes will have filler NPCs to take care of the maintenance tasks that players who are most likely to be attracted to those tribes are unlikely to be attracted to. I call the purposes of these maintenance tasks "social and economic homeostasis," in reference to the recent popularity of the "H" term.
Nerans may be the go-to tribe for people who are interested in homeostatic tasks, but there will also be some such tasks that only a few Neran fans, if any, will be attracted to. Who, after all, wants to take up night-soil carrying or night watchman-ing as a PC career? Who wants to be the lord high bumwiper (literally, not figuratively) for the king? Who wants to be a sculler? These are all employment positions that particular social and economic conditions have required, and there are many more like them.
I think the reliance on NPCs as direct or indirect participants in combat will rule out raiding-only careers. Janoans in particular gain social status from hunting prowess. Hunting prowess requires more than just combat skills. I recall that Janoans are not considered fully adult until they kill a dangerous beast and wear its hide. Thus, a Janoan that was not a successful and highly skilled hunter would not have the prestige to put together a warband that was sufficient to raid neighbors with.
I am considering the unfeasibility of raiding-only careers, or at least raiding-only careers without a "tail" of non-hostile homeostatic support. Maybe I'll start a thread about it, when I've thought it through a bit more.