If you substitute Rondo in for Westbrook, that Thunder team probably doesn't make it out of the first round. Westbrook is definitely a better overall basketball talent, and he is the better athlete.
Westbrook averaged 7-8 more points a game in Thunder losses than he did in Thunder wins. He was probably around 19-20 in the wins, which is 2-3 points a game more than Rondo was putting up before he was injured. In games where he took more than 20 shots the Thunder were 2-4, as opposed to 7-0 when he takes 20 or less. Yesterday he had a Rondo-like stat line and the Thunder dismantled the Grizzlies. Rondo could easily make them a better offensive team.
Just a quick update on this courtesy nba.com statcube, since the second round is over for both players.
The Thunder are a +57 with Westbrook playing, and a -5 with him on the bench. The Celts were, oddly enough, the same +57 with Rondo playing, but they were -45 with Rondo on the bench. Side note, in the Miami series, Rondo played 97 minutes before his elbow injury. We were a +15 in that time. He was on the bench for 27 minutes up to that point, and we were a -25 in those minutes.
Statcube highlights areas that are more than 10% different with a player in a game or on the bench:
With Westbrook playing the team takes and makes fewer 3 point shots at a lower percentage, takes and makes more free throws, gets more offensive and overall rebounds, gets fewer assists and fewer steals but more blocks.
With Rondo playing the Celts have a better overall fg%, make more threes on fewer shots (percentage goes from 23% to 54% with Rondo playing), take more free throws, get more offensive, defensive and overall rebounds, more assists, steals and blocks.