A couple weeks ago my LS decided to do a couple Chapter 1 runs for the people that wanted to finish their AF/Relic reforged head gear. They didn't have a 6th person and couldn't find a healer so I spoke up and asked if I could come PUP if I brought my auto as support healer on a Normal difficulty just to help them make things easy. They agreed to let me go reluctantly and we started the fights.
We went three fights in a row without any problems with my auto support healing, which was pretty nice, but they didn't expect much. Then the next person who put in their orb thought it would be fun to put it on difficult and everyone thought we were screwed. We went for broke and started the fight, but the best part is: My auto kept up with the healing and the fight went by swimmingly. Granted it took us about 10-15 minutes, but still there were no problems.
For people out there that like to play PUP and try to be PUP only. It can be done, just takes some convincing and hard work.
BTW! I'm not a well geared PUP and I don't even have a WS set yet >.> between helping others and being lazy it's kind of a work in progress for the past 4 years.