I understand the idea of minimalist solutions and low parts count. But remembering that the speaker motor/diaphragm/cabinet is a system that has many filters, sometimes having a part of two in the circuit counteracts reactances and makes the system as a whole more pure.

I really like keeping it simple, and sometimes that's best. Phil's little speakers sound great just bolting the speaker in the box. But there are other systems that are definitely improved with passive compensation. And it's not necessarily a matter of quality, or of artificially "fixing" a driver's response. It's just the way linear systems act.