I hope to see success for Moxy, as competition is lacking after all of the mergers.
However, I don't hold your hatred for our large airports, or even yours as well.
DEN, no alternative other than COS, which I use frequently. LAX, plenty of other options. ORD, easy options already exist to the north, including MKE and MSN. IAD, BWI and DCA. The list goes on, and I frequently use those options, but sometimes my work is close to the airport, and ORD for example works well for me. I've never had issues flying in and out of ORD, and I don't find the cost nearly as extreme as you suggest. I also prefer larger airports, because it often has a club I can visit to get some work done, and some free drinks or coffee, and be on my way. If things go sideways, I have a ton of options with a major airline to get rebooked on that simply don't exist in small markets and I assume Moxy won't have any interline agreements. And if I really want flexibility I'll buy another airplane and go back to flying myself around the country just as I did years ago, assuming my wife doesn't see the expenses.
SYD and MEL, never felt like it was a big deal between the airport and the city, but maybe that's just me.
Back to the states, my parents lived in Maui years ago, with my father working daily in Oahu. Apparently not as shocking as some would think, as he often mentioned him and about 20 others did the exact same flights every day. Kapalua (JHM) offers flights to HNL, but the times are not convenient and the cost is higher. So smaller airports may be closer or cheaper to park at, but offer inconvenient flights and sometimes higher cost.
In my perfect world, we would have an airport between COS and DEN for commercial aircraft, but I likely have a better chance of winning the lottery before that happens, despite the demand that I think would exist. My drive times to DEN are 60 minutes, covered parking at a remote location is around $14, quick ride in the van and via CLEAR and PreCheck I'm at the gate pretty quick. COS is 30 minutes drive, free valet parking (sort of, I pay a yearly fee), but not covered parking, so I'm screwed if it hails. That happens so often in Colorado that it's not a question of if, but when... That said, easy airport, and at most I'm 5 minutes from car to gate. However I just don't see the economies of scale working for a COS-XYZ airport that isn't large. Someday, Colorado Springs will actually be the largest city in Colorado, but that won't change our airport options, it simply means traffic will suck. I can't speak to Australia's views, but getting a new airport or even expanding a current GA airport for commercial operations in the states is such an uphill battle that DEN might be the last "new" airport we will ever see.