So what happens when a rich baron approaches a farmer who's exact GPS ownership record is registered on the blockchain and says "transfer digital ownership of your land to me, or i kill your sister"?
Exactly the same thing as what happens without a blockchain.
Weak institutions are absolutely a problem in human society, but they are not solved by decentralization technology.
Even better for the land owner, they (or more likely a "subcontractor") can force the transfer once and even if courts get involved and decide in favor of the farmer, the records can't be corrected if they are based on blockchain technology.
A less violent example would be a fraud based on social engineering.
It sounds like you’re throwing hands up and stating that no change is possible.
Land records are by definition ledgers. A distributed ledger is also a ledger. Does it protect you from a physical harm? Of course not.
Weak institutions are a problem, but technolgy can be used to strengthen them. If you can make facts more available and easier to access, perhaps you can push disputes to local magistrates and improve access to justice.
Exactly the same thing as what happens without a blockchain.
Weak institutions are absolutely a problem in human society, but they are not solved by decentralization technology.