> here is how I can share a file from my phone to any other phone in the same Wifi.

This will not work on many public and corporate networks. A common place where you’d want to share.

> surely there is an opportunity create a simpler UI!

It’ll still suck compared to Airdrop. Apple has gone to a lot of trouble to make that work as well as it does. Trying to setup something relying on temporary hotspots will be sub par UX. (And a nonstarter for Apple devices - user apps can’t touch the WiFi settings).