I apparently didn't pay that much attention to the fifth ST movie, but if I recall correctly they were going to the center of our galaxy, while in the two TOS episodes you mentioned they were going to the edge?
1) They were still going to the center in "Magicks".
2) The distances involved might be different or equal; the edge might be close to Earth in some interpretations, but the core cannot be argued to be that.
3) Yet they were not going to the center
as much as they were going to
the center, italics on the fact that they did not necessarily travel all the way in that direction. The heading is more important to the respective plots than the distance traveled!