Remove applications from 'cmd'+'tab'
I'm pretty sure the Dock and App switcher are linked together, you can't get what you want. It's unfortunate because many apps are simply background apps that are irrelevant in people's day to day workflow.

You can however, opt for a 3rd party Window Switcher, which can be configured to not show applications that have no open windows. Some people like Witch, I very much like contextsformac. I have it setup as OptionTab, but you can replace CommandTab entirely if you want.