DPH BM is okay, dph hit decent damage on AA/LA class. don't see much dph bm cuz of the low accuracy on r8 unless your lucky with reroll, and yes demon bm can dph but dph will be literally useless against any HA class.just click any skill > hope for gof
be sure to keep specific range with the cleric if u got too much far from the cleric u die,use leaps forward and back wisely if needed and what the ppl above me said alreadydemon bm can be dph if u get double/tripple str on each piece of r8 gear get as much str as u can... and u will be dph
Going full str r8 stats is not a good idea. It leaves you massively vulnerable. The best thing to do is to use r8 for defensive stats, and str engraves to achieve a higher damage output. You need a set of +2 def, and a set of +20/22 str. This way you can swap safely and easily between tanking and damage. He could have a full str set and a defensive set. However, if he's not using macros or scripts, I don't recommend it. Too risky during mass/group pk since you will get a lot of focus. Full str would be decent in 1v1s against LA/AA classes though.
...based on my observation demon BM is better than sage...
I'm glad you enjoy your demon. With sage I have just 3.33 base APS,which becomes 4.00 when quicken stone in my claws activates.(Demon spark and quicken stone don't stack.)I'd prolly get more with r8. This is with dragon.I like my sage because activation of quicken stone doesn't overridemy boosts from sage spark.It is possible to make very nice DPH demon,but sage DPH still hits a tiny bit harder.