There can be several scenarios where controller just won't be as capable for reaction or movement.

From pala example: the pala gap closer (charge) to avoid a mechanic. Mobility is a big thing in instanced content, specially raids, rotating a controller just makes life much harder.

Not to say, training your muscle memory to use a controller and later using mouse for a different class is probably not optimal if the case would be to use controller only for paladin.

and yes, Godsent law may also require fast reaction and aim in specific scenarios where the defence buff is required in specific locations where controller would just make it slower and harder to place.