There's a lot of things that went wrong here... not all of them can be blamed on LAN (although I agree that they could have been a little more efficient in anticipating everything)

Nowadays, arriving in SCL outside of your original time slot in a narrowbody does cause this issues. SCL is very over capacity for years now and the expansions needed 5 years ago are just starting. This is a government and airport operator issue.

The buses (not being the usual airport bus but a "regular" bus) is the airport operator's fault. The airlines do not operate these buses.

The terminal doors being closed where you were dropped is a miscoordination of the airport operator and the airline. LAN should have made sure (by proper coordination with the airport management) you could enter the terminal as soon as leaving the bus, even though both the bus and the terminal access are responsibility of the operator.

Sorry you had to experience this. Not using a proper jetway is a PITA all by itself, let alone all the rest of the stuff you went through. The good thing is that this is more the exception than the norm (not the jetway thing, but the rest) and eventually, as the airport capacity is increased in the coming years, these problems should tend to happen less and less.