I can give a little context just from my experience renting an apartment there. The large Jeonse where it is the price of the property is not necessarily required. Usually it is still usually rather large, and the higher the jeonse the less the rent is. So you are correct that a jeonse the cost of the house itself would usually mean $0 rent, whereas a more "normal" 1 years worth of rent jeonse would yield you a "normal" rent.

The huge deposits are not held in escrow (though they should be), but as I found out after having to sue to get my Jeonse back, there are ways to protect it if you act in advance:

1) You can register a lean on the property when you first move in in the amount of your jeonse. 2) Do NOT vacate the property until the Jeonse is returned.

That being said, people are mostly just trusting and I don't know of anyone that actually follows those steps. As a foreigner you are especially vulnerable since they know you likely have a flight to catch on your move out week and won't hold the property hostage. That being said, the legal system for these kinds of debts was swift and we got paid quite quickly once a lawyer was involved.

The whole state of Jeonse is quite extraordinary. It has a huge effect on people being able to move away from home, and I would guess a large effect on homelessness overall. It is wild that you have to pay $30,000 USD to just move into a 1 bedroom apartment. I had a small studio near a university and it was $12,000 USD just to move in.

If I do it again I will definitely be prepared for filing a lien and for a fight at move out.