But on this northern tour in particular, Williams has been superb on the carry, on defence, and now firmly regained his attacking mojo. In an incredibly tense victory at Murrayfield, his offload to a flying McKenzie helped create Beauden Barrett's crucial second half try.
And for the second time he completely deceived the defence by taking the ball right to the line before, at the last second, dropping a perfectly-weighted grubber into the in-goal - just as league playmakers do dozens of times each match.
At 32, it seems Williams is charting a similar path to All Blacks centurion Ma'a Nonu, his world-class predecessor at second five-eighth. As Nonu's career progressed he, too, developed kicking options; his distribution also evolving to the point it became one of his major strengths.
When Nonu started as a raw Wellington wing, few envisioned him adding such skills. Likewise Williams, a big, strong, tall man, is growing more confident to bust out things we haven't really seen from him previously.
Good players make the grade; great players are never satisfied.
Returning to the XV-man game from Achilles surgery, Williams endured a slow start to this season. But even his biggest detractors must now admit, if only through gritted teeth, he is back near his best. Eliminate the discipline errors and Williams cannot be faulted.
"It just shows how hard Sonny works on his game along with all the other midfielders we work hard on developing and getting better as players," Crotty said. "What you're seeing with Sonny's kicking that's something he's spent a long time practising and that's why when I got a dot off one of his kicks last week I was so excited to see that hard work come to fruition in the big moment.
"It's one of the most satisfying things in rugby when you work hard on something and then it comes off in a game."
Even with Ngani Laumape, Anton Lienert-Brown and Jack Goodhue at their disposal, the All Blacks never had any doubt about their premier midfield pairing. Faith is now being repaid.
Not only are Williams and Crotty beginning to click in a big way on the field so, too, does their relationship continue to strengthen off it. That bodes well for this week in Cardiff, and next year when the cavalry return.
"He just goes about his work and doesn't let public opinion get in his way. He's a diligent worker; the way he leads physically and looks after himself in the gym. It would be nice to see some accolades, some positive stuff, because he's been working bloody hard and it's awesome to see that.
"I probably don't understand well enough how the New Zealand public perceives him but from what I know he is a good friend, a good team-mate. He works hard and he's a good man to play alongside."
