Maybe it's not so much about if someone can shift their feelings with choosing thoughts and direct them toward joy, but rather if one believes they are going to feel a certain way no matter what or not.
That what you guys are debating is more about believing exact fate or believing your thoughts create what you are getting.
One person will say nothing is fate, everything is up to you, such that if you guide your thoughts you can get into any state of feeling and this feels like you get to choose all your feelings.
Another will say feelings are part of nature and in response to what fate/life is giving me.
Now, which belief is victim hood? And which is delusional? And which is accurate and natural? And which generates more frustration? And which makes you think you are in complete control? And which would bring more peace? Which is accepting? Which is fighting?