You are correct, distributions like Kubuntu are not TRULY community-driven as they are still subject to Canonical’s influence. Anyone saying otherwise is merely being pedantic.

However it’s not Canonical who’s running Kubuntu, it’s the community, they have the power to revert Canonical’s bad decisions, sadly by giving themselves an increasingly higher workload. Most distributions will simply give up at some point, for example VanillaOS’ next release will be based on Debian as it was getting too tough to remove snap and all the bad things Canonical adds.

Kubuntu uses snaps which are largely disrespected by the community, that’s the end result of being under Canonical’s influence. They can’t rebase on Debian without effectively killing their raison d’etre and they don’t want to remove Snap, perhaps because it would be difficult but most likely because they’re deep under Canonical’s influence, they look up to Canonical to some extent.

This is, in fact, the very meaning of “influence”. It’s even worse, in fact, much, much worse for Fedora, they have been culturally enslaved by Red Hat, sorry for the strong word.

what would happen to distribution X if Canonical suddeny made Ubuntu closed-source?

I believe Linux Mint has done some planning for if Ubuntu does something like that - probably to rebase off Debian in that case

It boils down to who and why someone is distributing the software to you. A corporation expects to eventually get some profits out of its actions, so it’ll sometimes do things against the best interests of the users, because they benefit itself; on the other hand you expect a community-driven distro to be made by a bunch of people who just want to use the software, and have a vision on how it’s supposed to be.

Canonical suddeny made Ubuntu closed-source?

Canonical can’t make Ubuntu closed-source. Most of the code in Ubuntu was not made by Canonical, but by third party developers; Canonical is just grabbing that code and gluing it together into a distro. And most of those third party devs released their code as open source, and under the condition that derivative works should be also open source (the GNU General Public License - note, I’m oversimplifying it).

What Canonical could do is to exploit some loophole of the license in the software from those third party devs; that’s basically what Red Hat is trying to do. In the short term, people would likely shift to Linux Mint (itself an Ubuntu fork) or make their own forks; and in the long term, fork another Debian derivative to build their new distros from it. (Or adopt Linux Mint Debian Edition.)

The key is in the name. Whoever distributes the software to you determines whether it’s commercial or community. Where they get it from is irrelevant because they’re the ones distributing it to you.

Ubuntu can’t be made closed-source because of the licensing of the software they use from upstream. Red Hat is still not closed source, for instance. Everyone who gets it gets access to the source code. But if Ubuntu went away or whatever then downstream distributions would be in a spot of trouble. They could rebase on Debian (which is what Ubuntu is based upon), but how hard that would be varies wildly depending on distro. Linux Mint already have a Debian edition, for instance. No problem there. Pop OS would certainly be able to make it work as well; they’re a very professional operation. But take, for example, Endeavour OS. It’s Arch with a graphical installer and some nice defaults. Without Arch Linux (which is almost certainly not going anywhere and is a community distro) they’d have some real problems. There’s no upstream to Arch to rebase on. They’d have to so fundamentally change everything to accomodate a whole new base and packaging system that they’d basically be making a whole new distro.

From what I understand and to continue your example of Ubuntu-based distros:

As you say, Ubuntu itself is corporate-driven, so there are things in there that exist pretty much solely to benefit Canonical (e.g the telemetry they recently introduced if i recall correctly)

Most of the time when basing distros off of others, I think it’s to keep a lot of features - either to save dev time or because they only want to tweak a small portion of the distro and not write a new one from scratch.

Because devs can modify the entire codebase, they can remove features that are corporate-driven (telemetry and such) and effectively create something fully (or mostly) compatible yet without such features.

Another major example imo is the removal of snaps, which most people (myself included) strongly dislike - as far as I’m aware removing them in Ubuntu itself is quite a difficult process as it’s baked into the distro itself. I imagine a lot of people want something like Ubuntu as it is quite friendly and has one of the lower bars of entry for Linux, but object to corporate things like telemetry and the overall monstrosity that is snaps.

Apologies, i went down a bit of a tangent, but I hope that roughly answers your question!