Darksiders Blades & Whip Pack

Bundles are a special discount on a set of products. If you already own some of the products contained in the bundle, purchasing the bundle will allow you to "complete the set", paying only for the products you don't already own while still receiving the full bundle discount on each of those products.

no , you just complete your set with the missing items , if you can wait till sale you can get the Deluxe version of darksiders 3 for 30 dollars at 50% discount like last time if you go for the full franchise pack

If this is for the current deal on Humble, try asking Humble support to make sure.
But I'm fairly sure those franchise pack keys that map to a Steam Bundle come in single keys.

There were only ever a small handful [like, 5 or so?] of packages that ever gave gift copies with prior ownership, and all of those explicitly stated that they did so (and the vast majority were from Valve's own packages). Ever since they disabled inventory storage of gifts and introduced bundles, even that small handful seem to have had that function disabled.

As far as activating keys from other sites, they'd simply activate the same way their steam store listing would. Well, to address that simply, it should reliably be safe to just assume a key activation isn't ever going to give gift copies for prior ownership [though there are games like Frozen Synapse and Space Farmers that'll give a gift copy regardless of prior ownership, so it's not impossible for keys to generate gift copies]. Rather, the thing to look for is if it's actually just a single key being given out, or if it's an individual key for each component. There'll actually be good odds of the latter for a bundle listing, since [to the best of my knowledge] you can't make keys for bundle listings, meaning the publisher'd either have to create a comparable package listing or simply offer the keys up individually, to create a comparable psudeo-package.

For things like this, it's always best to confirm directly with the retailler you're looking at, since it'll be something that typically only they can definitively answer. In some occasions, you can get your answer by checking against steamdb listings, by seeing if a comparable package exists or not. That said, there does seem to be a non-bundle package listing for the Blades & Whip compilation on Steamdb, Humble implies it's a single key, and a quick google search implies the same; So there's not good odds for you getting a positive answer.

What you could perhaps try doing is seeing if anyone'd want to trade D3 for the franchise pack- but that'd be a fair bit of a hassle, and unlikely to be particularly favorable if the aim is getting something out of the trade.

Thanks for the explanations. I see the odds are low. On the other hand, there's no risk for me as well.
both deluxe D3 and B&W pack go for $35 at HB (with 10% off extra for monthly subscribers)

If I finally decide to buy, I'll be sure to let you all know the results