I'd say don't start off as a gunslinger for your first class rather than make an absolutely worthless agi based build that can't do anything and won't ever get parties. Desperado GS are good DD in AL3 parties, and you can still use Full Blast in TV1 like >this. With such a build you'll do a sizeable amount of damage in WoE, too, whereas any agi build will die in seconds due to their horrible HP mod. While you probably can't read the text I encourage you to look at the pictures of euRO GS in >this thread, where you'll see nothing but dex/vit/int Desperado GS, without a single agi based one for a good reason.
Can't see first link, but I have a pic about my build (Which is in a very-low quality screenie)

Maximize to see my stats and equipment
AGI/DEX/Crit GS builds are NOT weak builds as you guys mentioned, they can do ~1k Damage at 190 ASPD easly on Atroce(And other mobs) on a low-rate server (That was the test server w/ legit stats and equipment), GS have a crappy HP mod because they are made mainly for ranged, not leeroy-jenkins-ing up to the boss without any decent strategy and pot spamming (Hell, low-agi pistol users won't be able to carry shields nor evade, that means you are deadmeat), plus, Agi/Dex/Crit builds are cheaper than that one that you suggested because of pot spamming, the agi/dex and crit WILL require some sp-recovery items for buff though, and by your survival comment, GS cannot equip shields without de-equiping their guns, and to desperado you need to close range the target(Desp is about 7x7 area around you), and each transclass have a skill that can easy kill non-thara users easly at low range (Cart Termination, Spiral Pierce, Sonic Blow, Sacrificial Ritual, etc), But AGI builds can flinchlock a transcharacter into place, before saying about Madness Canceler and Gatling Fever's movespeed reductions, you will need a good tank, as an Expanded Range class sucks at tanking (A LK with alice and raydrik is a pretty good tank), but my point is, you will die alot by trying to kill a high-tier mobs due to their habit of spamming AoE attacks, while as an AGI/DEX/Crit build, you could easly stay in a safe area shooting a target monster without worrying about things like Storm Gust or Pulse Strike that the mob was intended to use at the target, most mobs nowadays are big and hard to put down exp givers so desperado won't be as much as good as Agi/Dex/Luk build in endgame, and about your parties thing, usually some people avoid calling expanded classes for their MvP parties, anyway, the choice is the topic creator's, those screenies on rocards are mainly about PvM mobbing, no MvPing so far, Full Blaster is still a good choice but it has a very nasty after-cast delay and a 65 SP cost at maximum level, taking out that the 23k in kasa was a lexed hit(proberly) and the dancers "A service for you" was used to cover it's SP flaw, anyway, this is just my opinion, shun other builds just because your build is "the best" and you think it's flaws are minimum, but I prefer to use GS as a Archer/Hunter/Sniper type. Eveen though most people on euRO think that desp is the best,