That is not really true.
Activity regarding past months should be similar. If those who are in the top have trade just a few trades, that's because they have trade also very little in the past.
You can look at activity as another criteria to be on the top.
On the other hand, as they signal in the page, they take into account return, but also uses D-Score to rank all the darwins.
If it is discouranging to you, keep working. Doing good you will be there at sometime.
At the end, it is dawinex the one who is investing his money into Darwins who win DarwiniA, so I think it is unffair to tell them how to rank those darwins.