You can think what you like, but the bullet did not tumble because the wound tract is straight and a tumbling bullet will follow an erratic path.
As you can think what you like. It is a points like this that I bow to the experts and when people like Fackler talk about bullet tumbling I listen. So yeah I believe they tumble.
One of the reasons it did not tumble is because of the rotational velocity of the bullet that keeps it stable. By the time that the bullet looses enough momentum to continue to penetrate, the rotational velocity has also nearly finished and the bullet is now unstable..
Rotational velocity is quickly lost as the bullet expands. The dirty profile of the post expansion bullet throws a whole new set of variables into the equation totally changing the preconceived notions. The forward motion is still present and as Newton Law states continues on in a straight line.
It is funny but the two things we want most from a bullet expansion and penetration are mutually exclusive.