Ideally table plugin should be aware of css properties ( that comes from stylesheets ) and show correct border styles. Especial if your customers rely on backwards comparability ( document created with CK version x should render same with CK version x+1 ). If those css values needs to be changed in future, it can be very complicated for projects relying on CK editor to update versions, without introducing subtle bugs. Both plugin and default css values comes from CK editor. I think for developers to start changing default css values is a big no-no.
Adding tables with full borders is how other editors works, it is intuitive and users already familiar with table feature from other products. Majority of our tables will have borders only very few (most of them are needed for layout purposes will be partially or fully invisible ). Our use case, that I tried to explain in closed issue, is that we want to add table with borders by default and allow users to change selected borders as none ( invisible ) as needed ( this functionality is working in CK4, we are migrating to CK5 and this is breaking deal for us ).
Close reason was duplicate, but it isn't. Issue #6363 was closed and this issue was created.
