Global shortcut to switch to instance of application without selecting window

The Super+0/ ... /9 combination actually triggers the action set for mouse click on application icons in Ubuntu dock. In your case it's set to 'window previews' and so the key combination shows window previews.

If you set another action for mouse click you would see a different behaviour. For example, if you run the following command in Terminal it would just raise the window closest to the foreground as you wish:

gsettings set org.gnome.shell.extensions.dash-to-dock click-action 'skip'

(Note that as mentioned above it would also change the behaviour on mouse click on application icons.)

As mentioned by @vanadium in comments below, another alternative is to use the cycle-windows option. This option also raises the first window on click (or pressing the hotkey), but if you repeat the click (or the hotkey), other windows of the same app are consecutively raised. To set this option, run

gsettings set org.gnome.shell.extensions.dash-to-dock click-action 'cycle-windows'