So Bloggs let me guess, you're from WA and that's pretty much where most of your flying has been ?
You obviously have " no idea " how airspace runs outside your little bubble.
Busy places like Europe ? I assume you've never flown into Beijing or Shanghai ? And as far as I am aware, no, they don't use COBTs and slot times in "busy" Europe. BTW Beijing is far busier than any European airport, if you ever left WA you might have known this.
As far as my faux paw (sic), that is an " average " movements per hour for a SINGLE runway airport versus a " max " number of 24 for a 2 runway airport which I am told gets reduced to 16 when inst app in use. Gatwick handles around 4 times the traffic per month that Perth does.
PS you don't even have to travel the world to find these things out just enter " google " into your browser.....or I guess, ignorance is bliss.