the biggest frustration i have as a fairly casual (and extremely scrubby player) with DAMP is how frelling gear dependant it is. in short, the major difference between ME3MP and DAMP is power damage. the damage from your tech/space magic in ME3MP was what it was; whereas damage from your powers/magic magic in DAMP is keyed to your weapons. you take a max level fury out in ME3MP, you don't even need a gun, let alone a good one. you're just going to make biotic boom-booms and they will destroy your enemies. whereas you take a maxed out elementalist out and unleash a rain of fireballs on your foes...well, if you have a crappy staff, it's just going to tickle them.
couple that gear (and promotion) dependency with the fact that rare and unique are absolutely meaningless in DAMP, and you get the interminable grind mechanic. now, i don't mind grinding so much in SP. likewise, i see the value of a level 8 unique weapon...in SP. in MP, it kills the fun. i never promoted in ME3MP, unless i wanted to respec and didn't have any cards. and so what? why does DAMP want to force me to constantly relevel my character? fun, joyful gameplay is what will keep me coming back. not an interminable grind to make my gigantic warrior with a BFS actually feel powerful and not be felled by a single arrow.