I'm sorry you are frustrated with Arrows - they are quickly becoming the control that people think needs the most love. We are discussing how we can make arrows better for you guys and I've included your feedback in that discussion thread.
You can, however, use the arrow to make a line. All you need to do is remove the heads of the arrow by de-selecting them in the inspector:
There is also a horizontal rule and vertical rule (search for rule in the quick add) if you don't need any angle in your line.
Does that work for you? Keep the feedback coming because we want to make arrows better for everyone. If anyone else has arrow suggestions, post them here and we will track them!