Given what a mess shipping has been for the last two years, they appear to be taking the "underpromise, overdeliver" route on shipping quotes.
In some cases you're finding far flung regions relative to the source having better availability, because they were allocated a percentage of the original supply but are also too far away for scalpers to be interested, so they just haven't gone through it as fast. Australia hasn't had too many troubles with some items that are pretty hard to get elsewhere for example. Getting a 3080 in NYC is probably a real challenge, but I can walk to my local parts store and pick one up no dramas.
They're all using the exact same CPU, in fact you can make the air perform (almost) just as well as the pro/mini by opening it up and adding a thermal pad: https://www.cultofmac.com/759693/thermal-mod-m1-macbook-air/
Honestly 16GB Air is pretty epic for $1200, though you probably want to spend the extra $200 for a storage bump as well. I'm very happy with the performance for dev tasks, and with my (displaylink) dock it runs multiple screens just fine too.
Custom build Mac Studio, on the other hand, takes 10-12 weeks.