All very true, no doubt that the passenger experience would be enhanced with a station actually at the airport but I have travelled through Gatwick where after arriving at Gatwick station I have then had to walk through the south terminal to catch a transit train to get to the north terminal.
The Stansted passenger experience would be enhanced if it did not take up to 59 minutes to get to London and had a direct link to more than just 2 London stations, which means for most passengers another rail journey either by train or underground once in London. Also trains to and from Stansted don’t run through the night.