GB is having a bumper year at home that's for sure.
AUS definitely had a bad pool year and with all the medals in swimming they suffer. There is a reason swimmers tend to occupy the biggest individual hauls: lots of events, all pretty much the same, so no real specialization ...e.g. marathoners simply do not run the 100m dash. So if a country happens to have a couple of that years standout swimmers, they are going to make a real haul.
USA usually fairs pretty well in track as well as swimming, but their mens mid-distance seems to be having a very off year (no qualifiers for Men's 400 e.g. an event they swept 4 years ago).
The breadth of GB's competitiveness is the remarkable thing this year.