To what extent is an MBA a "rebranding opportunity," and how much are you judged on your past in recruiting?

The MBA is often characterized as a "rebranding opportunity" for people looking to change careers or gain access to more competitive/prestigious recruiting, which I believe implies that you're given a "blank canvas" on which to build. But to what extent is this actually true?

For example, let's say you're accepted to a top 20 MBA with less-than-great work experience, and you want to recruit for IB/Consulting. Are you really treated as a fresh-faced student, or are you constrained by what your work experience was before you went back to school? Basically, how important is your work experience in MBA recruiting?

Obviously lots of nuance to this question so curious to hear any opinions.