Phil,
id prefer to have simple words yet the post on mix powder i must admit has got me thinking about this once more - CA (who im big fan) always said the gap was in the base.
SoberRat's post on mix pwdr re started my thoughts.
what does making a different a base do was my 1st thought. i can only describe as going to a different BIR. it's still BIR but tates slightly different.
2nd was using a different mix - what does this do. this is now pushing my ability to describe. i would say it gives or not gives BIR. whether added as 1 (ie mix) or many makes no difference if accurately done. as example the IFFU staff curry has 8:1 coriander:cumin. this is long way from BIR taste.
which is more important is the question. i dont think you can say. both are equally important.
the experience does count in making base. both real McCoy BIR bases ive tasted are better than what i produce today despite significant effort. putting the finger on why is very underestimated.