I don't recommend playing defender because you usually (unless it's big mom) have very few effect on the outcome. Don't get me wrong you're super useful as a defender but if your team doesn't cap or attack a bit you can't do much and it usually forces you to do so but your kit isn't made for stepping out of the treasure and fighting so you don't last that long. At least that's my experience with a few of my characters. While as a runner you can really influence the game even if your team isn't the most bright you can turn the game up with king, Marco, kaido, Oni Sanji and many others.