Linux Mint downloads (briefly) compromised

It looks more like they took Ubuntu, added their packages, and called it a distribution.

I don't think I understand what you think a distribution is. Do you thing Ubuntu isn't a distribution? If Ubuntu is a distribution, and Linux Mint took it, added their packages, and re-distributed it under their own branding, how is Linux Mint *not* a distribution? Yes, it is most definitely a fork of Ubuntu, but a fork of a distribution is a still a distribution. I think you're underestimating how far the Linux Mint fork has diverged from Ubuntu, but regardless, even if it was a very close fork w/ very small differences, how would it not be a distribution? And how is the Ubuntu fork from Debian any different from the Linux Mint from from Ubuntu?

I had been thinking you were conflating Linux Mint w/ their Cinnamon DE, but now I'm just confused by what you mean by distribution.

My definition of a Linux Distribution is: a project to distribute the Linux kernel together with a selection of user-space packages. Linux Mint fits that definition.

Most distributions, including Linux Mint, have a set of goals that guide which user-space packages they select for inclusion, and they put effort into getting the user-space packages to serve those goals & deliver a consistent user experience. But while I think those goals are important in determining how useful a specific distribution is, I don't think they're defining charateristics required to be a "Linux Distribution". If someone distributed the Linux Kernel together w/ a completely random selection of user-space packages w/ no effort spent on consistency, I would say that still fits the definition of a "Linux Distribution" - it would just be a particularly useless one.

What is the larger scope here? What is it in Mint apart from the installer and the desktop environment that differs from regular Ubuntu or Debian?

I was comparing the scope of the Cinnamon DE to the scope of the entire Linux Mint distribution; not the scope of Linux Mint to the scope of Ubuntu or Debian. To me it's very obvious that Linux Mint is larger than one package within it.

Again, I think you're underestimating how far Linux Mint has diverged since their fork. There are many more differences between Linux Mint & Ubuntu or Debian than just the installer & desktop environment (and the DE isn't really different, since you can use Cinnamon or MATE in Debian or Ubuntu). But again I don't think that's relevant to whether or not Linux Mint is a distribution.

What makes Linux Mint different are its different goals, and the different decisions made in pursuit of those goals. Its goals are out-of-the-box ease-of-use & a traditional desktop computer user experience. While Ubuntu also has a goal of out-of-the-box ease-of-use, they don't have the second goal. And Debian has many more goals & different priorities. Both Ubuntu and Debian do have broader goals & therefore larger scope than Linux Mint.

Another significant difference is the project's organization: here Linux Mint is closer to Debian than Ubuntu, being a volunteer non-corporate organization, but compared to Debian is *much* smaller & less mature.

As a result of the nature of Linux Mint's small volunteer organization, they made the decision to clone much (but not all) of the Ubuntu repository directly, rather than investing in the infrastructure to completely build their own repository. I can understand how the cost/benefit analysis appeared that led to that decision, but I think it was a mistake, compounded by other mistakes made later (see glaubitz & h2 comments earlier).

But while I think Linux Mint has made mistakes that ultimately lead me not to use it, even when I agree w/ their goals, that doesn't mean they're not a distribution.