Oh they are, but it suits different needs and uses. Like knife skills are great for support and are viable in that sense, just not the best damaging skills. All weapons are viable, they just aren't meant to cover every single aspect you want. They fall under damage and support roles and although they can do both, they fit either niche better.
Assault Rifles are good for debuffs and taunts, but I don't see them being a huge damage dealer in the long term. You definitely can use them, I just think there are better alternatives when it comes to doing damage vs. support.
For me I went with Dual Guns/Swords and right of the bat you know that your swords will be your main source of damage while the guns are there to support and buff.
For the sniper build, most of your damage comes from your sniper rifle rather than your javelin. You can use the javelin, it just isn't as productive for doing damage and is there to help rack up TP through melee combos.