Gunslingers, along with the other extended classes, are meant to overachieve ONLY the first classes.
So gunslingers should be able to defeat an archer, and hold up it's own against a sniper/hunter decently.
Taekwon can probably takedown a swordsman + merchant and be able to fight fairly against a a knight/crusader/blacksmith.
Ninja can kill a thief or mage easily, and fight against an assassin/rogue or a wizard/sage.
Extended classes were never meant to be as good as the originals.
So keep that in mind.
This is only true for below average players. Consider every char i mention after this high lvl(85-99) with decent to great gear.
A star glad is one of the best emp breakers(id call it third after edp sinxs and zerk lordknights). It can do very good pvp damage points and ive taken out good players using advanced classes quite consistantly(and mind you i dont play on high rates or over 99 stat/lvl so this is legitamate type servers im talking). They do have trouble against certain classes but all classes do.
Taekwon ranker has enough hp to tank just about anything and can be very helpfull in woe by breaking the precast using that tanking ability(20k+ hp.. yes please), good aspd and the High jump skill(can get around the castles faster than anyone by jumping onto the snipeing points). For pvp they arent quite as good but with good gears they can beat some advanced classes.
Soul linker is not meant to pvp but they can raise their teams power so much that it doesnt matter. Great class to have around especially if its built for woe(mid int 100 vit mid-high dex no attack skill). And if you pair it with another soul linker the opposing guilds may as well not even precast.
Ninja.. magic is broken just in case you didnt know. Ice bolt is doing 100% matk per bolt instead of 70% like its supposed to. Its broken like this on officials to but it will be a while before its fixed. Their bolt skills have NO aftercast unlike mage ones. Fire formation is a great slowdown technique for woe as is Hidden water(use this in a precast.. only tk classes should get by if everyone concentrates. The 3rd tier wind skill goes OVER magnetic earth and has NO CAST TIME.. not to mention its a WIND skill.. This makes your precast MUCH MUCH stronger due to the wind skill breaking the sg freeze as well as killing/slowing down enemys if they manage to drop magnet earth. The third tier fire skill does great damage and is extremely nasty with a strings bard.
Gunslinger. Gattling for locking, statusing and emp breaking is good but its a very fragile build. Shotgun can afford to get a good amount of vit, do very respectable ranged damage, has a huge radius atk for the times where its usefull(11x11) and can use grenade launcher to set seriously damageing traps which also status. BTW try full buster with a strings bard, blue pots and a proper weapon and build.

These classes werent meant to be worse or better than originals, they are like any class in that they have shortcomings and advantages. They each can do things that no other class can do.
The only way to reduce FA damage is to be resistant to Neutral attacks (ala Ghostring, Raydric, Harpy, etc.), and those typically aren't in the hands of every player.
Thara and poo/berret/etc also lower FA damage. Not for sure if alligator cards and long mace do as well.