The thing with the s-foils on the ARC were that they technically weren't even S-Foils... There's no weaponry on the ends of them for a wider fire pattern or anything.
And as far as it being reminiscent of the X-Wing, other than the shape they open to, that's my beef... They're really nothing like the X-Wing's are other than the shape! MANY ships have folding wings. V-19's, B-Wings, ships from The Old Republic, ships from The New Republic, ships from The Republic, and how many shuttles now?
I think it's probably something done for a variety of reasons... space constraints when out of service (ala planes on an aircraft carrier), maneuverability improvements (either in space or not), wider firing patterns for weaponry, "heat dissipation" (I can buy it), etc.
To me it's like walkers... It's not a lineage because a walker has 2 legs, so it must be related to all walkers with 2 legs. That's like saying anything rolling on tracks is the same, when the reality is the vehicle may be an APC, it may be a tank destroyer, it may be mobile artillery, it may be a multi-purpose piece of armor, it may be a tractor for towing heavier equipment... not to mention if it is a tank, it may be a light tank, heavy tank, medium tank, etc.
It was another shining example of oversimplification of the visuals for marketing purposes. I hated that. And to that end the ARC-170 and AT-RT failed on every level but simplistic similarities to have a true tie to OT vehicles.
That's a big raeson the Y-Wing would've worked on an epic level... It just needed to be the CW armored version in the Prequals for it to have worked perfectly as a ship you would recognize, that had been stripped down to bare bones by the time of the Alliance... It would stand as a testament that it could still compete that long past its "hey day" as a military craft. The same with the Z-95 but more tied to the EU past it has since it would ultimately be a wholely different fighter to the X-Wing (and EU just ties them together as from the same manufacturer and many of the 95's features being carried over into the X-Wing's new space superiority fighter design, blah blah blah).
The AT-PT, for my money, just makes more sense. It still wouldn't have been a further step to the AT-ST as I see them as wholely separate purposes, but it would've been an incredibly cooler design than some guy riding a walking moped into battle.
Sadly the cartoon's actually made the RT cooler by making it quite nimble, so I can buy it as a weapon of war, but to me it does nothing better than a Speederbike with ultimately a similar goal in mind. Speed, agility, etc., while still giving a small weapons platform. I suppose one could argue that it is a better static mobile gun (think like having the little gun that drops out of the Falcon for Han to clear away his ship from danger) to do infantry support, than a speederbike would be, but it's still got an exposed operator which makes it a very unsafe thing to just stop and start shooting with it trying to support some infantry in the process.
Maybe the antenna's boost communication signals for infantry squads that are near it?
I've been thinking about that, and "counter-jamming" issues since communication jamming does come up in Star Wars some.