Everybody is looking for the magic bullet, the self sustaining high performance backyard meat bird. Somewhere it is written that the Delaware, among others, was this bird. But the new ones from the hatchery won't work, you have to get the "old timey" lines. To put things in perspective, the "Old Timey" Delawares are not all that old timey. They were made in 1940, fell out of favor in 1960. They were made from crossing two breeds that weren't really all that old themselves. In a lot of these cases, the newly made "breeds" were still riding the hybrid vigor train, being that they were barely stabilized composite breeds. Then someone wrote about them and so it is gospel, until this day.
 
I'm not detracting from anyone who has worked hard to build performance traits into birds through the years. I'm just pointing out that hybrid vigor is a powerful thing. The beauty of the Cornish X is not that it is some magical cross. If that were the case, you could cross any hatchery Cornish with any Plymouth Rock and get outstanding meat birds, which doesn't seem to be the case. The secret to their success is that they have two very carefully selected lines, that have been maintained pure for a very long time, with no outcrosses. Their performance is gauged by how they perform as a cross.
 
In a backyard set-up, it might work better to focus on a cross that you can make, rather than try to keep one breed that does it all, according to evidence that was documented when that breed was still riding the coat-tails of hybrid vigor itself. Unless of course you want to work with preserving a breed, which will be quite more involved than just raising a few for the freezer.
 
With some of the new genetics that breeders have available  a click away on the internet, it is possible that someone could come up with a composite breed that could outperform the "old timey" Delawares, or maybe even the most famous of all composite breeds, the pure Cornish itself, born of simple people just randomly crossing a bunch of radically different stuff together.