Stats don't say everything. To label them the best side? How can you do it? Like back then, it's pretty well known that Easts and Souths pretty much owned the NSWRL..
Thats why Wests were defending premiers in 1935, and Newtown ditto in 1934. The best defending side in 35 was Saints, then Easts then Wests - all within 9 points of each other.
Comparing sides and players of different eras is a terribly subjective thing. There are so many variables to calculate. You mention quality of the opposition - how about training measures for a start? iMHO the only way you can compare sides from different eras is by judging sides on their achievements against other sides. You can only do that by stats. Obiously the better sides will be revealed this way. Same with players.
Thats why it's f*cking stupid to say this current Roosters side, as good as it is - is their best ever. It never dominated like the 1935 side did. Nore was it unbeatable like the 75 side. That pack had 5 players who played test football during their career - probably the best second rowers to pack together in a team - Beetson and Coote. They had test halves. They had 3 current or future internationals in the backline, and amazingly had 2 gun backs injured - Harris and Fairfax.
This Roosters side has dominated - but in a year when a few traditionally strong sides were in rebuilding phase. Its a great side.
But it's done nothing to make it stand out in the history books like their 75, 35 or even 11-13 or 02-04 sides. If it loses it will be forgotten in few years.