Backstab: What I don't like about it and how I "fixed" it.

Let me just say it's not a bad move, but it has a few problems that don't really jive well with my idea of the fiction, and how I think thieves should work. Here's the default rule:

When you attack a surprised or defenseless enemy with a melee weapon, you can choose to deal your damage or roll+DEX. *On a 10+ choose two. *On a 7–9 choose one.

• You don’t get into melee with them
• You deal your damage+1d6 
• You create an advantage, +1 forward to you or an ally acting on it
• Reduce their armor by 1 until they repair it 
• Use a bit of gear for another effect that fits within the fiction

What got me even thinking about it in the first place is a player asked me [sic] "would that provide any bonus? sneaking around attacking a creature from its opposite flank? or would it be just the same as running up and punching it in its smug face?" Initially, I couldn't really answer the question, or at least didn't answer it correctly.

I said no, DW doesn't do that per se, your situational bonuses are in moves. But then I read closer "you create an advantage, +1 forward (etc)." Alright, that's all well and good, but they rightly pointed out "surprised and defenseless". So it dawned on me that the onus is upon me to determine every time whether a foe is surprised and/or defenseless, and I thought the way to do that was Defy Danger. I didn't like that.

Next there was "you can choose to deal your damage or roll +Dex", then choose 1-2 options, one of which is damage with a bonus, and a couple others have nothing to do with hitting anyone. So I  removed the redundant option, and wrote the following "replacement" move for use in my games:

Skullduggery

When you engage in tricky underhanded tactics, roll+Something*. *On a 10+ choose 3 different options. *On a 7-9 choose 2.

• You don’t get into melee with them
• You deal your damage+1d6
• You create an advantage, +1 forward to you or an ally acting on it
• Reduce their armor by 1 until they repair it(edited)

*Depends on how you describe the tactics.

It removes the need for me as a GM to define if the opponent is surprised (that can be an assumption behind "tricky underhanded tactics", but it doesn't have to be) and make the player roll Defy Danger. It doesn't force the player to strike immediately, and allows them to represent flanking or planning as appropriate with +1 forward. And finally, I prefer "choose 3/choose 2" over "choose 2/choose 1"

Is it broken? Probably, but I thought Backstab was broken in the other way (in being too narrowly defined).