Or command+click because up until osx, or even way later than that macOS didnt even had rightclick.
The Mac introduced right click with System 8 in 1997. The keyboard equivalent is ctrl-click, by the way - not command click.
Why does the finder half asses this interaction (and moving a folder up) while moving the cursor and selecting/unselecting items is done like on other plattforms?
Not sure what you mean. Holding shift while using the keyboard (or mouse) will let you select multiple contiguous items. Hold cmd to select items dotted about.
Not really, CMD-O for open, together with CMD-C for copy, CMD-V for paste etc were introduced in 1982 with the Apple Lisa.
As I say, Finder is primarily designed to be mouse driven, so most people will be using double-click to open, otherwise CMD-O is your friend.
The good news There is a tiny bit of freeware available called “PresButan” that will let you modify the Finder behaviour match your preferences. You can grab it here: http://briankendall.net/presButan/index.htm