David Gerrold entertained the idea of away teams as early as 1973, in his book The World of Star Trek
. He proposed the first officer lead the team, with the captain staying on the bridge. Apparently he was able to push some of these ideas during TNG's first season. But as others have said, realism doesn't always equal effective drama. Your top-billed actor as captain is eventually going to grow tired of missing out on all the action scenes.