I can't agree with you on the grounds of this very problem. A raid boss is a static entity with a predetermined difficulty and a researchable behavior. The players in a battleground come in various classes, specs, talent setups, experience levels and skill levels. You cannot simply know what a group of 10-to-25 players are going to do in every instance immediately upon entering a match. Feng isn't going to stop in the middle of Phase 2 after he realizes he can easily kill the healers if he focuses on them and then easily finish the rest of the party. A few players from the opposing team may notice a Holy Paladin slightly behind a group of DPS players and see an opening to chain-CC and burst that healer down with a variety of methods not necessarily predictable by your own team.
They aren't rewarding you for "almost being good enough to win." They're rewarding you for nearly matching another group of player's skills but ultimately losing. It's incentive to keep trying when you're on a losing streak.