If you think you have a better notation idea for 128-bit numbers, build your own address converter and try it?
The obvious other notations for numbers that large to compare to are the various notations people use for UUIDs/GUIDs.
I personally find IPv6's designed notations one of the easier ones to use, especially because of that :: fill with zeroes shortcut to focus on the easier separation of prefix versus suffix. (For a network you control you likely only need to remember the prefix, and then suffix is whatever numbering scheme you want to implement so it may be algorithmic and simply ordered ::1, ::2, ::3, etc. Also, the regular pattern of a colon every four hex digits versus say the strange group order of UUIDs is nice. Trying to write the notation of a UUID without software help is much more painful than IPv6 address notation, I think.) But also, I have a bit of dyscalculia (my brain catches all the individual digits in a number but not always their correct order) and hex works much better for me at remembering or visualizing long numbers.
Even having them be 16-bit integers would've been find imo