My initial answer to the unanswered question:
Shift right can be used to improve testing process. Can shift left exist without shift right?
I think it can, for sure. What you’ll end up with will be respectable: you’ll be efficient at your testing, you’ll have the developers involved, you’ll release with confidence, and you’ll probably achieve some measure of stability. It can be rewarding enough in and of itself.
What “shifting right” gives you is “wisdom”: are you testing the right thing? Are you spending too much energy on things the users don’t care about? Are you testing your software the way your users test it? Are there some insights you can gain by taking the post-release analytics traffic into account?
Shift left can exist without shift right, but in my opinion you’ll be left with a missing puzzle piece: one that you may not even realize has been missing until you inquire about it.
Shifting right gives you a virtual guarantee that your testing is guided by what the business (i.e. the CEO) cares about.
Hope that helps!