Should I keep my Runescape Pure, or get def on that account?

I had a main but i don't use him anymore, so this is my only account. I'm constantly getting pissed off about how little I can do without def, but i like having that ability to PK with a lot of other pures. Also, if I get def, my stats will be extremely crappy. Stats ATM: 1 def, 70 str, 50 att, 80 mage, 76 range, 44 prayer 69 hp. What should I do?