This is seriously weird. Back before pipermail was integrated into mailman, my understanding is that the then-current version was the best available MLM archive tool, heads and shoulders above everything else -- especially mhonarc. Moreover, my understanding was that pipermail had only improved significantly beyond where it was at the time of initial integration.
Has mhonarc improved so much in the meantime that it has now overtaken the current version of pipermail?
Try it for yourself. Maybe your needs are different. But if I want an archiver that will process huge mbox file from other systems - without crapping out, will decode encoded binary attachments, have flexible, customizable output, etc., I can't think of anything else I would rather use. If MHonarc is so bad, why do so many people go the extra lengths currently required in order to use it instead of pipermail?
As I say, it works for me. And very well. Maybe worth a second look? If you try it again let me know what you find.