Actually no chickens are GMO. All breeds have been developed by selective breeding, even the hybrid meat chickens and the hybrid commercial layers. A hen can only lay one egg a day because that’s how long it takes for an egg to go through the hen’s internal egg making factory. The meat ones grow so fast now that their body has trouble keeping up. Their heart can’t take it and quits or their skeleton breaks down. If they grew any faster they would not live to butcher age. They have been able to achieve all that by selective breeding. There is just no reason to go to the expense of GMO on chickens. Why spend money when you don’t have to? That’s bad business.
I’ll mention something else too. In the US no chickens are fed growth hormones. Hormones were banned for chickens in the late 1950’s. It’s still legal for most other animals but not for chickens. I know you occasionally see people advertise that their chicken is hormone free and they are telling the truth. But their competitors’ chicken does not have hormones either. Are they really being that honest?
I think I’ve seen what you are calling tumors on a very few chickens. I don’t raise the meaties, dual purpose instead, so it’s not just limited to the meaties. It’s right on the breastbone. It looks like a tumor but I’m not sure if it is or maybe they bruised it when jumping on something. It’s in the right place to be a bruise.
About half the chickens that hatch are males. Until they grow up and become roosters we call them cockerels. They do have testicles. The ones you saw were probably really small. When they mature the testicles can approach the size of your thumb.
I don’t know who told you they don’t lay eggs or what they were talking about. Every one of those chickens was hatched from an egg. If you restrict their feed so they don’t grow fast enough to eat themselves to death the females can and will lay eggs. Maybe they meant that they are not good for eggs because they generally don’t live long enough to lay?
Several members of this forum have tried keeping meaties and get eggs from them, though they normally don’t live long lives. One person even said they had one go broody.