the mishna in sheviis 10:3 says a loan with a pruzbul is not cancelled, and that hillel instituted the pruzbul because people were holding back from lending. and ribbis is an issur deoraisa but the whole heter iska exists so business can run with something that works like interest.

so the question: why did the torah forbid these things in the first place if chazal were going to build a kosher way around them? and what is the point of a loophole, is it that the din is really about something deeper and the loophole keeps that, or is the prohibition just not meant for the real world?

bottom line: how does a person know when a workaround is the halacha working as intended, and when it is just getting around the point?