Here's an extra 2 cents and sort of a question...doesn't the capon get bigger than young birds? If so, the food expended on getting the bird to an older age would be cost effective in that respect~more feed, more money, but yields more meat and~supposedly, just as tender as a young bird? Don't know because I've never done it nor eaten a capon, but it seems much like cutting a bull calf and for much the same reasons. Sure, you could just eat that calf when it was really young and avoid all that cutting and time to grow it out, but you'd also have less meat than growing it out to butchering size and that meat would have a different taste/quality.
Say, if you fed two birds~one caponed, the other not~for 8 months and the capon turned out bigger than the uncut male, with more fat throughout the meat, on the same amount of food, wouldn't this be an efficient use of that time and money? Eating young birds only saves money but it yields less meat, so if one wanted a bigger bird but one that put on more meat/fat during the time it was held over, wouldn't that be as broad as it is long? It would also have the benefit of not having to be penned separately from the flock due to mating/fighting issues, so it wouldn't require more money in that regard either.
To me, saying it's more efficient cost wise to eat a young bird doesn't make much sense...small money, small bird. More feed/money, bigger bird. In the end, same amount of money spent per pound of meat, I would imagine, but the quality of meat(more fat within the meat fibers?) would be different/better/?.