To believe that the Rehnquist Court was more conservative (or less liberal) than the Roberts Court, one would have to judge Roberts to be more liberal than O’Connor, which is risible. As disappointing (or traitorous—choose your adjective) as Roberts has been in the two Obamacare cases and the California SSM case, O’Connor was far, far wiorse, clearly more liberal than Kennedy (who is *much* more liberal than Roberts).
George W. Bush’s two SCOTUS appointments (Roberts and Alito, the latter of whom has been outstanding, with fewer unfortunate votes than Scalia or Thomas over the past few years) have been, as a whole, far better and much more conservative than were George H.W. Bush’s two appointments (the excellent Thomas and the execrable ultraliberal Souter) or Ronald Reagan’s three appointments (the outstanding Scalia, untrustworthy moderate Kennedy and liberal-to-moderate O’Connor. George W. Bush’s lower-court appointments also have proven to be excellent, better than his father’s and up there with President Reagan’s. George W. Bush had many flaws, but his record regarding judges was very good (even though he did, as you noted, luck into nominating him instead of the enigmatic lackey Harriet Miers).
I believe Roberts is to the right of O'Connor, and for that matter, Warren Burger was to the right of her as well. O'Connor was a pretty partisan lifelong Republican, but she veered leftward on numerous important issues. As I noted, freepers should be more disappointed with Reagan giving us O'Connor than giving us Kennedy.
Again, its not a matter of the judges individual idealogy (agree that Alito, Thomas, and Scalia are individually more conservative than Rehnquist, O'Connor, and Kennedy), but a leadership issue.
Rehnquist was a powerful conservative advocate and was able to sway the rest of the justices in a way that Roberts and Burger are not. Reagan saw this and was wise to elevate Rehnquist from Associate to Chief. It works the same way under liberal CJ's. The court got a ton of "landmark" liberal ruilings under Earl Warren because he was a forceful liberal advocate who was able to sway other justices (both Democrats and Republicans) to his POV, and have the decisions written in way that reflected his agenda. On other hand, Harlan F. Stone, a FDR appointee as CJ (and a former associate justice appointed by Coolidge... bad decision on Cal's part) was liberal as well, but wasn't nearly as effective as CJ, and his court left little mark on U.S. history.