Cutting/copying the entire line is a feature commonly found in programming editors, like Visual Studio Code or JetBrains’ various IDEA-based IDEs. The feature can be very useful there because when programmers start moving code around, it’s often a line-based process (i.e., you don’t want just part of line). However, even in such environments, users can almost always turn off line-based clipboard operations because many find it an annoying feature.
In an app that’s more often used for long-form text, however, I’m not sure the feature makes sense. It’s absolutely a non-standard tweak to a behavior that most users rely on without any thought. Then again, given Obsidian gets used with so many types of content, I’m sure many folks actually are working with line-based content (such as various lists) and do/would find it useful. Myself, I didn’t realize the feature was there until I stumbled on it testing an automation macro I was building to create internal links with display text, and I realized my macro breaks in a particular scenario because of this feature. That said, I’d definitely find it helpful with some of the content I work with.
All of which is to say that I strongly agree that Obsidian should adhere to the standard cut/copy behaviors. It’s just not the type of software where most users won’t be surprised by line-based behaviors. But… I also think the line-based versions should remain available. Ideally, I think it should be available as a separate command so that it’s always available and its keystroke can be customized (perhaps the default should be something like cmd-opt-X/C).