I use my RCBS swage in a RockChucker press. It takes a lot of force to swage and you are going to have quite a bit of flex in that Lee (or any non-O shaped press).
Most new users of the RCBS swage combo bend the rod during the first use. Some never master proper set up. Take the time to read the instructions, sort your brass by headstamp, and go by feel. I have swaged over 10,000 223 rounds in my RCBS swage combo and never bent the rod. So it can be used successfully.