Suppose I had a specific area of interest I wanted to research about, but the few professors who currently work on it are NOT at top-ranking universities - would that make the business school's ranking a less important factor to worry about?

One of the paths I'm considering is, rather than working to rise the ranks to C-level, to establish myself as an expert within my current company/niche, as well as develop new theories and knowledge based on my experiences, and research/write books on the side, e.g. by seeking the possibility to do a strong/original Masters dissertation, and maybe DBA a few years later?

Does this make sense or could I be missing something?

You are missing something: few MBAs have the time or design to allow a seriously scholarly research project. Take the best MBA for your goal, ignoring where the specialists in your topic are. Read their papers and their co-authors' papers. Collect data in your professional life that will be useful to them, and then co-author with those academics. 

You are missing something: few MBAs have the time or design to allow a seriously scholarly research project. Take the best MBA for your goal, ignoring where the specialists in your topic are. Read their papers and their co-authors' papers. Collect data in your professional life that will be useful to them, and then co-author with those academics. 

Other things being equal, be close to thought leaders. However, other things are not equal. Choosing an interior school for your goals simply to be close to people who are easy to contact if approached thoughtfully makes no sense.