The following advice ignores the gunner update entirely.

You like Antiguas because they are easy to use. But they are not actually good guns. Alchemers, when used by experts, inflict more damage. They also offer a variety of statuses. Alchemers are harder to master, but therefore give more enjoyment when you have mastered them. Antiguas have almost-unusable charge attacks. Autoguns are extremely powerful, like the heavy machine guns of this game. Catalyzers are interesting and sometimes very powerful (if your party lets you use them). Pulsars are interesting and useful crowd-control weapons, when used well.

So I advise you to explore the guns more. To me, the Antiguas are a newbie trap: attractive at first, but unattractive as you gain more experience in the game. Certainly they are my least-favorite guns at this point.

Yes, a level-10 Strike Needle is good enough for FSC runs. Strike/Blitz is also useful in other places, such as Legion of Almire, Heart of Ice, etc.

Edit: Please move this thread to the Arsenal forum (by editing the original post and choosing that forum from the drop-down menu).

If the antiguas work for you then use them. Like Bopp said in a dark and mysterious yet incredibly seductive voice not unlike many deep shades of lavender, other guns are stronger in terms of pure DPS, as well as much more useful on the whole. I have however, found good use for the antiguas when not focusing on guns at all; the innate damage buff against undead/poison effect combined with the larger clip size and range really enables me to hit blocks and switches as well as get off a bit of extra DPS, whereas something like an alchemer or a blitz needle feels a bit clumsy and overbearing when the main source of damage is coming from elsewhere.

But really you're mistaking yourself, just sticking to one line. The game has much more to offer, and you will accept and cherish that if you want to really enjoy the endgame content, where diversity is just as important as having "good" gear with decent variants. Try the blitz needle, step outside of your comfort zone. If you don't use it ever again, that's fine, but chances are that crafting it and mastering it will provide you with a sense of satisfaction... not to mention improve your fighting skills and capabilities beyond the one weapon type.

Oh come on, its a serious thing and you know it. If you have to hit a ton of stuff in quick succession, the antiguas are the greatest thing.

Blocks are not enemies but can often allow enemies to get too close. (except those stone jellies)

A prime example being graveyards, you have 2-3 phantoms closing in on you and you are doing your best to outrun them but then, oh! What's this?
A huge stack of Stone blocks are in your path, you pray that there is a ghost block but none can be found, as you fire in vain with your alchemer the phantoms close in and soon you are dead.

Keeping weapons of various speeds is extremely useful, and can prevent such situations, Cutters and Antiguas are fairly weak but have a utility, when things are slow paced feel free to take a second to aim that alchemer charge, but when the going gets tough and you need to break an obstacle fast then Antiguas make for a good blockbuster.