Maybe. You can't backstab until 10 though
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1-9: Base weapon dmg cap of 10
10-19: cap of 14
20-30: cap of 30
So it comes down to whether that cap gets factored into a 14 dmg or 15 dmg weapon for purposes of backstab calculation, which is only possibly an issue until 20. It just frankly doesn't merit thinking about. I see what you were asking though and it is a good question.