Nothing is wrong with your rear wheel or tire. Your problem is more one of physics than mechanics.

When you do a hard braking, there's a weight shift to the front which reduces the force holding the rear wheel down and therefore the traction. The more braking G's you generate, the lower the rear wheel traction, until the wheel skids and you cannot get any more Gs in the system. The same happens with cars which is why car brakes are proportioned with 60% or more braking power sent to the front wheels, and even then rear wheels always lock up and skid first.

In order to stop in the shortest distance you must bring the front brakes into play, but the physics here are trickier. Increased Gs increase the front wheel load and traction, making more Gs possible until the weight transfer is enough to flip you over the bars. So the key is to use both brakes and modulate them, to prevent rear wheel skids and/or endos. It's easily learned, but even very experienced riders can have an adrenaline rush and punch down the front brake causing a front end flip.

When I lived and commuted in Manhattan, I got so good at this that in an emergency stop (like behind a taxi cab) I could lock the front wheel, lifting the rear wheel, swing a leg over the handle bar, and step off the bike catching it behind me with my right hand. It looked spectacular when done perfectly, but I've also landed on a few trunks in my life.

The only thing I can suggest is to practice hard braking, until you can feel the point at which a flip is about to start, then ease off the front brake enough to prevent it. Do this at low speed and work your way up to the critical point by degrees, so you don't injure yourself learning to prevent injury. (the Catch-22 of learning good bike handling). It's important that good brake modulation is drilled so that it's totally automatic because you don't have time to thing about it during a 3 millisecond emergency.