"Where can you put time on the boats behind you?"

Let me explain

Adding a reaching mark causes all of the boats on the course to saill the same way. They will all sail the same triangle. Where are the tactics in that other than trying to get clean air. Boats rarely pass eath other on reaches, from my personal experience.

By forcing all of the boats to sail the same triangle there are more risks for contact with other boats.

Also all the boats are sailing the same line so it is harder to pass boats, even slower ones.

Opening up the course doesn't give any boat an advantage but give you options. If you competor is on top of you can can jibe away. Can't do that on an ABC course.