Same mish mash as great scientists such as Lorentz and Poincare did

The twin assumes that his brother is " asleep at the wheel"
He is not
The interpretation of the measures is wrong but the prediction "my brother will look younger than me " is true

Also Lorentz and Poincare and even Maxwell, as you said yourself, kwew that c is a costant but they tried to explain the "light paradox " assuming that Time is absolute

The speed of ligh being a constant entails the relativism of time, ok that's true, but it is not a so straightforward conclusion