Why am I metagaming my RPG, especially in SP? In MMOs, when I'm in a guild, I'll build a character that the guild may need, unless it's a healer, I suck at 'em. In a SP game? I build what I want to play, and I take the companions that I like, or maybe don't hate all that much... My personal canon character in DA O is a female Dalish, that romanced Alistair, until he freaked out on her going into Redcliffe. After that, he spent all of his time in camp, despite not having another S/B warrior to tank encounters. I managed to complete the game just fine, on Nightmare difficulty, w/out him.
I don't spend a lot of time worrying about x encounter requiring y set up, because I'm more concerned about story beats than combat encounters. I'm not thinking about the "perfect party", but a party of characters that I'll "get along" with, for the most part, if such a party is available. In one of my DA O completions, for example, I destroyed the ashes, with Wynne and Leliana in the party, and when they objected, I talked both of them down, because that's what I built that character for, not that specific event, but to be a smooth talker. In another save, I had to kill both of them when I destroyed the ashes. So I don't spend a lot of time thinking about party makeup, instead, I focus on what I want my character to be in a particular playthrough, and do that. So when I'm playing a story driven cRPG, I don't think about filling any gaps at all.