I use Merrick Grammy's Pot Pie for Megan's normal food. I'm not sure why it is thought to be higher carb. I've gotten information directly from the manufacturer (who is very responsive to specific questions, by the way), and the carb content is not high. It's not super-low, such as 0-2%, but Janet & Binky's chart says it is 8%. The most recent information I got didn't have the carb values, of course, but the other values didn't look significantly different from what is in the charts, so I imagine the carb value is still about 8%. It's lower fat than Wellness, which seems to matter to Megan. (Both Cowboy Cookout and Grammy's Pot Pie are 42% fat, according to the charts.)
Turducken is 9% carb. I sometimes use it when I can't get Grammy's Pot Pie. Its higher fat but still not as high as Wellness.
I used to use Cowboy Cookout, which is a beef food, until it became evident that my asthma cat is highly allergic to it. Even licking the bowl after Megan was finished (when there would be no visible food left) was enough to provoke a coughing fit. Its makeup is indeed ideal, but Grammy's seems to suit Megan fine, and it's not dangerous for Darwin.
The values in Janet & Binky's charts are from 2007, so Merrick isn't a new food. Must just be new to your area.