I can't quite remember where I read this, but somebody was likening the episiotomy situation to a piece of fabric. Your perineum is like a piece of fabric. It's not that easy to tear it. But if you make a tiny little cut into it, it will rip very easily. That analogy makes a lot of sense to me.
Also a natural tear is usually jagged so it creates a lot mor surface area for the wound to heal again. And natural tears usually occur along blood vessels rather than through them.

I'd definitely opt for a natural tear rather than an episiotomy. But I'm sure that there are cases where it would look like a natural tear could be more destructive than an episiotomy. I know my midwife doesn't like doing unneccesary episiotomies, so I trust her to make that decision.