The overwhelming majority of users never replace the battery on any system anyway, hence as I said it is not really a downside to them. The minority that do is perpetually shrinking as individual battery life increases.
You can not get more runtime by carting around batteries
If you insist on the batteries being internal, then yes, but if like the parent post you are already willing to spend the money and cart around the weight, you can just buy one (or more) of the many external battery packs on the market. The portion of users for which even this is unacceptable compared to carting around 2-3 spare internal batteries must be staggeringly small.
You can not get more runtime by carting around batteries
If you insist on the batteries being internal, then yes, but if like the parent post you are already willing to spend the money and cart around the weight, you can just buy one (or more) of the many external battery packs on the market. The portion of users for which even this is unacceptable compared to carting around 2-3 spare internal batteries must be staggeringly small.