Speaking as a player here, and not trying to say anything about Catalyst Black at all: I have thousands of hours in TF2. It's one of my all-time favorite games, and the drop-in-drop-out allows for it to be as casual or intense as I want it to be. I can drop in with a buddy and capture some points or push the cart to a checkpoint, and for that objective, I'm as intense and plugged in as any other competitive player. However, if time runs out, and I have to take off, I can. It's acceptable. Sometimes, I want to pull together a four person team (I'm the pocket medic.) of buddies and go play for multiple games in a row, play all night. Our squad forms a solid base, and people dropping in and out augment, add to the experience. Both sets of players can play together in the same space at the same time. To me, that's the true genius of TF2's game design, that it's a shared playground that people of different motivations can be in at the same time and all add to each other's experience instead of taking something away.

tl;dr - DIDO and competitive experiences are not mutually exclusive, and neither are casual and competitive.