What Fallacy Is This?--That's Not Important

A makes an argument for claim X

B responds:  I don't think what's important is X.  What's important is that...Y.

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B's response is both dismissive of A and an attempt to change the subject.  

It seems like a case of people talking past each other, because they have different goals. 

So if this were a debate about COVID-19 measures, for instance, person A could be advocating for a lockdown, citing the need to 'save lives'. Person B could be advocating against lockdowns, citing the need to 'preserve the economy'. 

If person A presented their argument, it'd be fine for person B to explain why their goal is more important...as long as they explain why. As in, it would still have to be a counter to the original argument - either accepting that X is important, but less so than Y, or demonstrating that X actually isn't all that important. This way, both people in the conversation could advance different goals while still responding to one another - talking to, rather than past, each other. If they didn't, and simply tried to avoid the subject, this would fall under red herring.