Gene,
A few off-the-cuff observations from the guns I have owned over the years.

I have always used my open choked Darne 12 for skeet, hoping to get some practice in over the course of the summer, always shooting low gun, even on doubles. I find I shoot live, wild birds much better than clay birds with that gun. I don't suppose the practice hurts anything, and I never run all 25 of them with the gun. But, come fall, I get my share of birds with it.
I play with the 20 and the 28 and have much the same results. I've never hunted the 28, might give that a shot on grouse this fall. Got birds with the 20. Miss plenty of skeet targets with it too, but, it might be choked a bit tight for a skeet gun. The 28 and I can be a comedy sketch on occasion on the skeet field, but, I shot an 18 with it one night when the stars and the moon were all aligned somehow, I think. It isn't a common thing for me to shoot it well, but, I've had a few glimmers of good shooting, only on targets, with that tiny little 28.
Three of my guns have barrels 25" or so long, wish they were longer, but, that doesn't seem to be a huge factor for my hunting, mostly grouse and pheasants.
The fourth Darne 12 will likely be restocked to fit me in the near future. It is severely right hand cast, and, I'm a lefty, but, has longish barrels of maybe 27 1/2", and tighter chokes, and I want to stock it identicle to my short barreled open choked Darne 12.
I owned a 29" barreled 20 gauge R15 with a straight stock and modified and full chokes that I had a hard time missing birds and trap targets with, years ago. I sold it, a decision that haunts me to this day. In the same vein, I have a truly ugly pump gun, with a black painted stock and a nylon sling, that I almost never miss a bird on a trap field with. I wouldn't think to hunt live birds with it, mostly because it weighs about 8 lbs, but also because it is ugly. Really ugly. But, I'm all done selling guns I shoot really well.
I bounce back and fourth just fine between my Darnes and the other guns, likely a result of starting with a Darne in my early 20s. Guys who get to the game late sometimes have to spend a lot of time practicing their Darne shooting, and I know a few exteme examples who sell everything else and just use their Darne.
I'm not in that camp.
If all I ever shot were clay targets, I'd buy guns better suited to that work, I suppose. But, if there exists a better gun for pushing the roosters around a frozen cattail slew at sunset, when it is-2 degrees, or taking a poke at a fleeing gouse in heavy early cover, than a 25" barreled Darne 12 that weighs 6 lbs, I haven't found it. I've killed a lot of birds with that little 12.
If you are struggling with the Darne on targets, I wouldn't give up until you have a solid year or two of time shooting it. I think that is good advice with any new gun, but, especially with a Darne. Also, try some actual hunting with it before thowing in the towel.
I hope the gun works out well for you. Keep us posted.

Best,
Ted