Still no. If you're not reliably doing 15 damage you're not reliably killing multiple orcs in a turn.With great weapon fighting it is about the average damage. But sure, not every hit will kill an orc. Some do, some don't. And you're not guaranteed to hit either. But the point is that you can cleave through several orcs, not that you're guaranteed to. Your suggestions do not guarantee success either, and I don't think a rule should. We roll the dice for a reason after all.
If you're not killing multiple orcs every turn you're not fulfilling the fantasy of killing multiple orcs every turn.
OSR games which are even more gritty and "realistic" are willing to have base rules that fulfill this fantasy.