Is Anything Viable?
Yes. It also depends. What content are you trying to clear? What are you trying to achieve? Anything can clear overland content. As you get further up the end-game "ladder", you'll have to start looking into optimizing your builds to contribute to the group. Vet dungeons require a little bit of optimization, but most builds can get by.
DLC dungeons may require a little more.
Vet Craglorn trials a bit more, and so on.
In theory, many builds are viable to clear 99 percent of the content in the game. It's when you start getting into difficult achievements or goals like speed runs where you'll need to heavily optimize around your group. And even then, the "best" for one group is not going to be the "best" for another.
As for questions regarding various item sets and so forth being viable:
There is no easy answer to this question. This is because the definition of viable will vary depending on the content you're running and at what level of accomplishment you want to achieve. If you're running just solo content, for example, everything is viable. B
But if you're arming for trinity achievements (no death, speed run, HM), then you'll have to use very specific set-ups to get those achievements.
In addition, different group compositions require different sets. For example, Worm Cult is useless in a predominantly stamina DPS group.
Why All This Matters
We often get questions like "what's the meta composition" or "what's the best raid composition" for Trial X/Content X? And often we find ourselves under fire from various groups of players who accuse us of elitism or toxicity when we do give our input.
These kinds of questions are asked so often (we get these questions almost daily) it had to be put here. Usually most endgame players answer with either what our teams have run or what we think could be most optimal.
These questions however have several (complicated) overarching themes to them that have plagued a majority of the PvE playerbase and produced incredible social tensions between the different demographics of the game: How do I get better? Do I need to change to get better? Do I really have to play what I don't like? At what point do I sacrifice fun to get what I want?
To start, the concept of the PvE meta is heavily misunderstood by both those moving towards endgame PvE and those who are simply repulsed by such a concept.
Running "meta" or "BIS" doesn't necessarily ensure success or entail that it's only "my way or the highway" to achieve whatever you want to achieve. Whether it's a world record score, a trifecta achievement or just to clear content, the degree of optimization required will ALWAYS vary group to group as there are many factors including player skill.
With the advent of ESOLOGS, many groups have started to heavily imitate the higher end groups but some groups we've had to help often find themselves more crippled or worse off and become discouraged.
What works for one group does not always work for another. This needs to be emphasized.
While yes there are objectively better sets, better ways to pull numbers, better rotations, sometimes better classes, better compositions when compared to worse ones (like 12 magwardens vs a more optimized composition) there is never, for the majority of the playerbase, an absolute best composition so long as the basics are covered.
At a certain point we're not even sure what “best” would entail. Is it the composition and item setup of the team with the highest score? If so, what if a different team beats that score with just one additional different class and maybe incorporating a different set? What were the circumstances of that score? Better RNG? Mistakes? What if the group just wants to play safe for TTT? What if the group just wants a clear with people who just want to play their mains? What if it’s a beginner group? What if people can’t just get a handle on the classes? What if people are struggling to learn MK/Zens?
It is ironic that people blindly criticize the endgame community for "refusing to recognize" that there are multiple ways of setting oneself up for content. They can't recognize the fact that is exactly what the meta (most effective tactic available) is and that raid teams have always simply pursued the best options available to them through constant testing and if it happens to work out, other groups take note.
The prime examples of this irony is that despite the sheer majority of the playerbase claiming in the past that Templar tanking or Sorcerer healing or "X isn't good" has often been proven wrong by the very people they accuse of being "elitist" or "narrow-minded". It was indeed endgame players first that proved the viability and optimal aspects of playing Sorcerer healer, a Nightblade tank, a Templar tank and many many more things.
In the end, it's about finding the best setup for yourself and your group. There's always room for improvement and thus the meta changes for many people whether it's in one direction or another.
The best advice we can offer is to always ask why other groups are running what they are and critically think what would be best for your group rather than blindly following one example.