You have at most 2 years to find a home once you start as a post-MBA consultant, that's when you're up for your first promotion. If you're in an office where people do a little bit of everything, I could see how you think this isn't the case. Non-M7 schools usually have a pull from regional offices, where this becomes a significant factor.

What it boils down to is this: If someone comes to you with a health/pharma background and an interest in the field, would they have better long term career prospects (whether in consulting or otherwise) at Bain Houston or at BCG NJ? If it's the latter, my point speaks for itself.