Interceptions left and right?
Brady only threw 12 INTs all of last year to 40 TDs, and the first 8 games of the season, he threw only 4 picks to 20 TD's in 308 attempts (610 total). He also had more games with no picks (5) the first half of the season than the second half of the season (4)
So statistically speaking, Brady was better the first half of the season, under "that outdated system".