Then explain why for autos Torque is a better measure of acceleration / speed than HP?

Torque is good but I can’t because it is not really true.

If you look at the power/torque curves for your engine you will see that the power equals the torque times the rpm.
To put it another way, the torque is equal to the slope of the power curve.
So if you have lots of torque you will get lots of power. If you have lots of torque at lots of rpm you will get loads of power!

Diesel is preferred for trucks because of high torque.

High torque but over a limited rpm range, hence trucks have loads of gears to keep the engine rpm within the power band.
(The torque is the power divided by the rpm so high torgue at low rpm gives good power at low rpm.)

And I realize there is ways to convert the values.

It is not a conversion as such, it is two sides of the same coin since one is equal to the slope of the other.

Hope this is helpful 🙂