To play devil's advocate, we aren't owed jack shit. Upon purchasing the game, we're "owed" everything in the final release that we agreed to buy for $60. As there is no contract saying "I will pay $60 for these following scenes and features..." we get what they choose to put in the game. That's the implicit contract upon purchase. Sure, we expect developers to deliver the "full product", as nebulous a term as that is, and it's shitty when they don't, but there is no "owe".
Additionally, there are multiple reasons for companies to release DLC shortly after release. One reason is attention. If they let DLC go too long, then they lose potential sales because people see the DLC announced, they may go, "nah, I'm not going back to that game, I'm done". Another reason is the trade-in culture. Nowadays, a lot of people trade in single-player games when they're done, so for a developer to maximizes DLC sales, again, they need to do it quick. A last reason is the staggering of content completion and actual release dates. While LoS2 was recently released, according to Bergeron it went gold months ago. In fact, most games go gold significantly before release, so a bulk of the content in the DLC could very easily been worked on during that period between the original game going gold and the release date. That's why it is able to be released so soon after and yet not particularly feasible to be put into the game.
However, that being said, I miss unlockables and meaty expansion packs too. When Cox was giving his lines about optional bosses, I was definitely not thinking of a re-used challenge fight of an earlier boss. I suspect that either neither did he and it got cut, or he was just outright lying. I'm not sure what to think about his lies anymore.