IMO it doesn't matter. People don't read news on updates. Should they? Yes. Do they? No. Should they have to? Also no.
Linus's point is to never blame the end user for something the kernel changed. If you want software to have widespread adoption, adding homework to simple updates isn't how you do it. People don't want a hobby or something to babysit, they want an operating system. Debian will go out of their way to make in-release updates go as smooth as possible, but are willing to through out entire parts of functioning packages between releases.
But this isn't even about breaking things for the end user. This will create excessive amounts of noise on the upstream repo. People will say "Hey! My keepassxc broke!" and they report it to keepassxc, and not to Debian. To which keepassxc just has to constantly reply "no, debian changed this on you, this is not a bug." If Debian had to deal with the fall out of their own decisions, I would say "yeah, im not sure if i agree with the decision, but oh well"... But they are increasing the workload for other teams.
It is already happening. The debian dev's stance is "This will be painful for a year." But it will be painful for keepassxc, NOT debian. The keepassxc devs asked them to not do this. Debian's response might as well be "Im inflicting this pain on you, even though you've asked me not to. But on the plus side, it won't hurt me at all and it will only last a year for you." If they really have that much disdain for the project, they should just stop packaging it altogether.
So yeah, debian has the legal right to do whatever they want because keepassxc is open source. but "just because I can, and you cant legally stop me, and its extra work for you, not me" is kind of a jerk move. This is what drives FOSS contributors to get burnt out and abandon otherwise good projects.