I fillet the breasts out of all my home grown chickens, any breed, any age, and slice into bits and fry hot and fast in lots of butter and garlic and right at the end, the pan is deglazed with soy and lime juice - served over pasta and it is always good and while some are more tender than others, all of it is easy to chew.
The rest, depending upon my mood, is either simmered really really gently or jointed up and slow roasted with lots of liquid.
The only time I have come even close to a supermarket bird for roasting was when I did cornish cross and even with 16-week old birds (they were huge) the legs and thighs were tougher than expected and stringy.
I suspect that the birds in the supermarket are almost at the going off stage as they are sooooo floppy and that may have something to do with it.
Having grown up with store bought chicken THAT is the taste and texture I want in chicken, my birds taste fantastic but lots of them, esp the roosters, don't really taste like chicken!