If you were to compare all the teams who had only won 3 games or less in a season since 1908 (of which there are 108 sides) and ranked them all based on win % and points difference per game, you'd get a fairly accurrate portrayal as to which sides were the worst.
Well I did that. Here's the top ten starting from worst.
1937 University - Played 8, won 0, drew 0, lost 8, for 41, against 309
1921 University - Played 8, won 0, drew 0, lost 8, for 82, against 292
1935 University - Played 16, won 0, drew 0, lost 16, for 109, against 529
1920 Annandale - Played 13, won 0, drew 0, lost 13, for 59, against 382
1918 Annandale - Played 14, won 0, drew 0, lost 14, for 73, against 316
2016* Newcastle - Played 23, won 1, drew 1, lost 21, for 279, against 772
1966 Easts - Played 18, won 0, drew 0, lost 18, for 147, against 446
1936 University - Played 14, won 1, drew 0, lost 13, for 99, against 414
1946 Souths - Played 14, won 0, drew 0, lost 14, for 124, against 353
1910 Wests - Played 14, won 1, drew 0, lost 13, for 117, against 386
Other more recent sides:
13th - 1984 Wests - Played 24, won 1, drew 0, lost 23, for 244, against 620
15th - 1993 Gold Coast - Played 22, won 1, drew 0, lost 21, for 229, against 572
16th - 1995 North Queensland - Played 22, won 2, drew 0, lost 20, for 269, against 660
21st - 1999 Wests - Played 24, won 3, drew 0, lost 21, for 285, against 944
23rd - 1990 Souths - Played 22, won 2, drew 0, lost 20, for 302, against 652
30th - 1995 Parramatta - Played 22, won 3, drew 0, lost 19, for 310, against 690
35th - 1991 Gold Coast - Played 22, won 2, drew 1, lost 19, for 240, against 492
36th - 2006 Souths - Played 24, won 3, drew 0, lost 21, for 429, against 772
7 teams have been winless in a year
Only Wests in 1984 had won a game but had a worst win % than Newcastle. But if the Knights lose in Round 26, then that would change, so that the only sides who have had a worse win % in a season than the knights this year, are the 7 teams who never won a game all year.