I think this is not question about monophonic vs. polyphonic.
For example Radias' arpeggiator works like this:
It takes your (1st) chord to arpeggiator and runs it forwards and backward (like it is in Origin). "Latch" button on, you can take your hand out of the keyboard and still it does this arpeggiation. But when you've done that (you have taken your hand off), still running arpeggiator is ready for taking another set of tones. If you play one note, then you'll hear one note arpeggiating. If you play chord, then you'll hear chord arpeggiating.
IMO this is much more useful than one which is in Origin. If I had to choose, I'd take this Radias-like arpeggiator in Origin. But as I said, it would be great to have both: there are cases (or songs) when hold-button way is nice too. I might wanna start my arp with just one or two notes and then give it little by little few more notes (and all this is possible by giving them one by one). To be really useful, this option (let's cal it "latch/hold") should be possible to save in preset. So some preset would then work "latchlike" and other with "holdlike". If this is not possible, another way is to make it in system menu level, but this is not that effective. Or is there some button that could be used as "latch"?