[Soapy]

Narcus does its damage as fire damage, making it usually resisted to some degree.

All damage is resisted to some degree.

1. It relies on taking hits, if you have high Defense this means you're unable to maximize potential; and if you're running low Defense/DR to make the most of this it's extremely high risk, high reward (I.E. one of the more viable glass cannon methods, which even then it can be walled by high DEF/high RES depending on which damage source you're more concerned with). If the person-on-fire doesn't queue the fact they're a Narcus user and you need to be cautious of your DPS, there's not much hope to win to begin with.
2. Fire is the most counter-played element with a good number of Resist methods, ways to turn it into HEALING, there are also ways to nullify Narcus' on-hit effect (see Steel Aura from BK's tree).
3. "You deal as much damage as your enemy deals to you," is misleading in the fact like previously mentioned: the damage from a Narcus is -still- affected by Defensive Values.
4. Like Lolzy said, numbers would help (and I don't mean to cherry-pick them with a high STR build VS. a squishy character). Attempted band-wagoning with no proof or comparison(s) made from other viable damage methods or mention(s) of existing counterplay leaves a sour taste in my mouth for this thread.
5. Low Accuracy and niche Fitting Form opportunities were a limitation/trade-off for these swords

1. It relies only on taking hits. One can simply build pure HP and Hit, potentially with heals, to return nearly as much damage as they take for very little investment, and a fairly good chance of it actually being free if they happen to be running Duelist (riposte).
2. This is no longer true whatsoever. Fire is far from the most resisted element. Every character lost 10% fire resist with the talents change, Mechanation resistances were nerfed and they are much less common than before, Hyattr went from the most common race to one of the rarest, Red Letters are arguably rare now since the drop table is astronomically larger than it was before, Nihilist still does its job, Razing Salamander does it even better, and a mutated Narcus will still get +50 to Hit and strip all buffs and fire resistance prior to the effect proc while dealing pierce damage with the main attack.
3. All damage is reduced by defensive values. Are people honestly forgetful enough that they need to be reminded in every thread? Compare the Retaliate items which return 50% of the damage you take from a certain element, or the Retaliate skill which returns even less, using the actual most resisted element, at a momentum cost.
4. Buzzwords leave a sour taste in my mouth. What math do you need to see, exactly, for it to properly get through to you that returning 100% of damage dealt is not fine?
5. See point 1, the last bit of point 2, the existence of Plisfa's Masochism, and dodge's overall viability.