BA Fly Creek on AT- keep or swap now that I use trekking poles

If you like it, keep it.
You will have ample opportunities to swap.

Its not your gear that will get you to Maine.

Its your head.

Using hiking poles for your shelter sounds like a good idea, except that most people have some sort of pole failure at some point on the AT. I used and broke four poles in total during my thru-hike. I wouldn't want to rely on my poles for my shelter because during a trip that long it's inevitible that a pole will break eventually. The fly creek was a very popular tent on the AT and probably for good reason.

This forum is all about how to drop weight.

If you're asking should you switch from a 33 oz system (Fly creek) to a <16 oz system. Cuben fiber tarp (4 oz), Bug net 5 oz, optional-groundsheet,stakes&guylines. I think the answer is pretty simple in terms of the goals of this forum.

You asked about difference in weather durability. Most advocates on this forum have said that by changing the pitch angle/direction of your tarp, its just as good as a 3 season tent. On the AT, you don't really have much extreme weather since you're below the treeline for 95% of it.

The tradeoff really just comes down to convenience and comfort. A free standing tent like the Fly creek is really easy, takes very little thought to put together at the end of a long day. You can do it in the dark. It wont' matter which direction its facing. Hammocks are also relatively heavy compared to a Tarp. But you can hang them ANYWHERE practically. I've spent 30 minutes wandering around in the dark before trying to find a suitable tent site without stumps or roots underneath. Its less of an issue in the daylight.

17 oz is a nice bit to drop though. Might add 1-2 miles to your daily mileage. (made up numbers).

As stated above, the Fly Creek 1 is a simple and quick setup. It also requires a very small space to get it setup. If it fits you and your pack….keep it.
I have a cuben fiber Lightheart tent that's 19 oz. I also own a FC 1. 90% of the time I'll grab my FC 1 simply because of the ease to set it up and the amount of space required. I typically hike until dark and look for a small flat space to setup. The FC 1 works great for that.
I'm 5'-9" and also fit in it with no problems. Great little tent for the money. Like you I've never gotten wet in it. Oh….and I also hike with poles. I actually just broke one Friday. It's a Black Diamond Alpine Carbon Cork. I ordered a new bottom section for $15 from the Black Diamond site and I should get it this Wednesday…tomorrow. I must have 1,500 miles on the poles and this is my first broken one.

I also have a Fly Creek ul1 and a Zpacks hexamid. If I think it's going to rain, I bring my Fly Creek. I've used this tent for years and it really is bomber. I'm still new to the Hex and so I may come to realize that it's fine in a storm.

Stick with the Fly Creek. For hikes up to about a week on the AT I take a 9×7 cuben tarp with 2oz net tent and it works great. If I was going any longer than that I would seriously consider taking a double wall tent. When its the 12th day in a row of all day rain the ease and comfort is hard to pass up. Worrying about if the rain is changing direction, etc gets old with a tarp and most of the shaped tarps are sweat boxes when the humidity stays that high. YMMV

Ryan

+1 to Ryan's advice. I wish I could add a FC1 to my "quiver".

I would get a lighter set up if you have the money. It's a long trip. I would tire of carrying that heavy tent. The Zpacks offerings would be about half the weight, and I don't see much downside. I think they are just as storm worthy. You also have shelters on the AT. But again, I see no problems with a Zpacks or even more minimal shelter on the AT.

When you start your AT hike, it will be cold and rainy for a month or more. You probably would be drier in the FC, but when it gets damp it will weigh more. When you've been on the trail for a month or so, you might switch to the cuben tarp. I've hiked with both on the AT and I usually get damp in the Hexamid when the wind is up and it's a hard rain; however, it doesn't absorb water and doesn't gain much weight when it is packed after a rain like the FC does.

Mail the cuben to yourself somewhere–say, Damascus–switch out and mail the FC home from there.

Your feet will be more of a worry to you than your shelter …