If a TTW test for 40 games means a TTW test for 40 wins here, it should be changed. When doing a TTW test for 40 games, you record losses as well in order to find out winning rate, then calculate TTW on the won games.
Also, with the current rules, you could technically win 1 game and lose 39. That won't happen, but we could, however, get really bad decks or just plain rushes with bad win rates.