Restricting the scope to those two problems would remove 1/3 use-cases and around half of the pages required (going by the "The Birth of a Product" section's bullet point list). It's an interesting exercise to think of the absolute simplest way to solve a given problem. As the author had been "itching to build an app for a while", I think solving the problem was not the only goal here - fair enough.

A shared AirTag could probably take care of the location issue easily. I assume that in this scenario with exclusively trusted users, trading off privacy for the convenience might be worthwhile.

Neither are needed to solve the problem of "splitting the gas bill".