Let’s compare that with other options.
A Sword main-hand has the auto attack, and a utility type ability. It relies on the off-hand for any real offense. So with a dagger for example, the only real offense you have comes from the auto and the bugged out dual skill. Even assuming it were not bugged, this would still lead to you constantly spinning round and round your target with that one attack. The cripple is somewhat redundant when you already have the teleport sharing the same resource. Cloak and Dagger has solid utility, but no great interactivity between abilities because of the high cost and weak effect of the sword stealth ability.
Pistol off-hand has a similar situation with relying too heavily on Pistol Whip, though the two off-hand abilities are fairly solid and help round out the weapon. Without interactivity between the abilities though, it still is not interesting to use and has entirely too much Pistol Whip (which itself is a rather dull and straight forward ability).
Pistol Main-hand has a solid auto attack, but Body Shot is borderline useless for anything at all and makes the weapon significantly more shallow due to fewer options. The dual attack with a Dagger has decent utility, but it leaves the combination with no main non-auto attack. It’s also shallow due to only being useful specifically when trying to gain distance from a melee character and nothing else, which again becomes somewhat redundant when paired with the cripple from the dagger off-hand (which is overall superior and more versatile). Cloak and Dagger is the only saving grace for the offense of this combination due to the pistol having an effective stealth attack, but has large restrictions on how frequently it can be used, especially since its a melee ability on a ranged weapon.
Then let’s look at the Dagger main-hand. It has a solid auto-attack, and a decent resource attack with Leap Finisher status. So far so good. Except that Heart Seeker is meant as a finisher for dying opponents, while simultaneously operating with a low cost that encourages spamming. So if the opponent has high health, this isn’t much of an option. And when they’re low, you have to use a lot of it. Aside from the finisher status, its also a very straight-forward ability without much in the way of interesting mechanics.
With a Dagger as the off-hand, you end up with three separate attacks competing with each other with absolutely no interactivity between them. What this means is that, based upon your build, you pretty much just spam one of these attacks to the exclusion of the others, leaving your options extremely limited and making the whole thing incredibly boring and simple. Have a condition build? Spam Death Blossom. Have a stealth build or Hidden Killer? Spam Cloak and Dagger. Have anything else? Spam Heart Seeker. There is at least some mild variation in that you’ll rarely start out spamming Heart Seeker regardless of build, and with the first two you may still use Heart Seeker to finish someone off who’s nearly dead or to use a Combo Field.
The number of Combo Finishers available to this set up are fantastic, but you’ll have a hell of a time actually producing a Combo Field yourself to utilize this aspect. You absolutely have to rely on Utility slots for this, and even then there are only a couple capable of this; one of which has a long recharge and encourages NOT using the finisher attacks in it (since you should either be using Backstab or not attacking at all).
With a pistol in the off-hand you rely purely on your auto attack and Heart Seeker for damage. Heart Seeker also being terrible when the opponent’s health is high. So you have an attack meant to be used only to finish people who are low on health, and only your auto attack to get them low! That is likely the worst oversight of any combination the Thief has. You have solid utility, but complete garbage for damage. You can, at the very least, leap through the shadow field you can produce then Backstab someone to get them low, but this isn’t something you can easily quickly repeat or rely so heavily upon, and the initiative cost is massive for mediocre results.
You also lack any way to really stick to your target, since you have neither a cripple nor a reliable gap closer.
The one high point of this combination is that the abilities interact together well, between Gunpowder>Seeker giving stealth, and having an effective stealth attack.
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