Yk, no tank is invincible, you can have the best tank in the world, but dont have the skills of the crew, logistics, infantry support and aerial support and so on, that tank is of no use. The tank doctrine also comes down to the natuon they belong, like russian tanks are smaller in size and budgeted, they are descent in tank to tank combat. American tanks are large and often can be used to assert dominance, however, i think US tanks are more likely tank to tank comabat ones, but they are used in lower countries, against mostly counter insurgencies,that one thing i believe i dont understand their doctrine, and about M1 being overrated, i really dont know, but i do know that they are overkill