The question is: Does it make sense for a "coop" game like TD2, that you can be more efficient doing stuff solo then in a group? Just an example: Why should I do the daily missions (on challenge / heroic) in a group if this can take up to 20-25 minutes, when I could do it solo in 10-15 minutes?
PS: I am not talking about WT1 or something like this. This discussion is focused on WT5 people with optimized (and almost "perfect") builds.