I didn't respond to your "heresy" statement.
I'm always open for a little bit of heresy. In this case, if I just wanted to sort data, you're right. There are lots of options, perhaps some that are better than using APL. The problem for me is what I want to do with it after it's sorted, where APL seems a better choice.
I'm not keen, unless I have to, in stuffing the data from an APL variable into a SortedDictionary, then extracting it back into an APL cvar for further processing.
However I definitely agree with your general principle of not re-inventing the wheel, or trying to do in APL what .Net already does perfectly well.