iTunes 12.5+ plist setting for View As -> Songs by default?
I don't know how to change the default view mode for new playlists, but you can run a script like this in Script Editor to change the view mode of all existing playlists:

tell application "iTunes"
    user playlists whose special kind is none and smart is false
    repeat with p in result
        set view of browser window 1 to p
        tell application "System Events" to tell process "iTunes"
            click menu item "Songs" of menu 1 of menu item "View As" of menu 1 of menu bar item "View" of menu bar 1
        end tell
    end repeat
end tell


I use a script like the one below to create most new playlists. It requires GNU xargs and readlink which you can install by running brew install findutils coreutils.

osascript -e'on run {a}
    set l to {}
    repeat with f in (get paragraphs of a)
        set end of l to POSIX file f
    end repeat
    tell application "iTunes"
        if number of l is 1 then
            tell application "Finder" to set n to name of (item 1 of l as alias)
            delete playlists whose name is n
            set p to make new user playlist with properties {name:n}
        else
            set p to make new user playlist
        end if
        with timeout of 0 seconds -- don't exit with an error if the add command takes over 20 seconds
            add l to p
        end
        set view of browser window 1 to p
        tell application "System Events" to tell process "iTunes"
            click menu item "Songs" of menu 1 of menu item "View As" of menu 1 of menu bar item "View" of menu bar 1
        end tell
    end tell
end run' "$(printf %s\\n "${@-$(cat)}"|gxargs -rd\\n greadlink -f)"


If the System Events application is not on the list of applications in "System Preferences > Security &amp; Privacy > Privacy > Accessibility", the script above results in an error like this: 636:751: execution error: System Events got an error: osascript is not allowed assistive access. (-1719).