A bullet train holds 2x to 4x the passengers and loads in 2-5 minutes. I get they are very different. Those 2x to 4x passgeners load into 16 cars (so 16 doors). The baggage does not have to be stowed before take off nor do any cargo holds need to be loaded. The aisles are wider. Etc.

Still, as an example of the best possible case, it does make me wonder how much more efficient loading a plane could be. I can imagine some magic way to use all of the doors, even if in the short term it means walking on the tarmac to one of 4-6 stair cases.

Maybe it doesn't matter. I wonder if anyone has calculated if such a system would save (or lose) money.