My friend came to the opposite conclusion from the same data, which is an exciting example of how there are limits to what engineers control once their designs go out into the real world. Of course, my friend and I are both designers, so we're biased that it's always operator error.
The way I see it, the "right" way for the crew to configure the system is with the low voltage bus tie open and both sets of HV/LV transformer breakers closed. The low voltage bus should be set up with critical systems (ventilation, fuel, cooling, and steering systems, lights, etc.) having the redundant systems on opposite sides of the bus. So if one of the HV/LV transformers/breakers go down, you'll lose one vent fan, cooling pump, fuel pump, etc. but not the backup. You would have uninterrupted service.
The bus tie breaker is useful in the event that one of the transformers go down. In that emergency, you'd be able to restore full redundancy within a few minutes of the transformer going down. That protects you against an extremely unusual situation when the transformer went down and then the operating fuel pump went down later. It seems like it is better to have this as the backup scenario instead of the default scenario.
However, this is all speculation from far, far away from a non-expert who hasn't seen the system in operation or seen any manufacturer instructions. The NTSB will have a lot better info when they release the full investigation. It would be interesting to see what the switchboard manufacturer said to use as the default configuration.