Isn’t the answer to this question dependent on the context of the school? If the school offers 12 AP classes and you take all 12 (and presumably do well), it’s impressive in that you’ve taken in the most rigorous courses available in your school and you’ve excelled. On the other hand, if your school offers say 16 AP classes and you do 12, while other applicants from your school do all 16 and excel, your coursework may look less rigorous (but this is obviously only one of many parts of your application and it doesn’t mean that you will get rejected while the other applicants will get accepted).
Yet on the other hand, if your school offers just 4 AP classes and you take all 4 and do well, adcoms should understand that you have maxed out the opportunities available in your school - and you can then further enhance your learning (and show your genuine passion for learning) by taking classes at the local CC or free MOOCs.
This question is pretty insignificant then, because it depends greatly on context, and probably isn’t that important at all in the grand scheme of things.