His punch selection is down, so I can see him looking more one-dimensional in that regard, but he did make a few adjustments, as crude as they were. For example, in round 4, once he figured out Canelo's power, he simply timed him and would trade a punch to get one, this made Canelo tentative and he slid out of the fight significantly until the last 2-3 rounds. Golovkin also started throwing his right, not to land, but to walk Canelo into his left hand. This kept Canelo in front of Golovkin more often than Canelo would have liked (especially since he was slipping out his left side a lot early on).
Again, nothing on the level of Mayweather in terms of giving his opponent different 'looks' or adjustments throughout the fight (Golovkin was always pretty straightforward), but enough to pull Canelo out of the fight for about 6 rounds in a row.
I don't think he was flawless, even in his prime - he was always hittable - but now, one fight after another he is looking less decisive. Even though he didn't lose yet, the trend is that each fight from here on out will be close. A shame he was avoided for his prime years.
For a guy aging naturally at 35 and taking VADA testing, it's normal. Big names have dodged him until now, and there's no surprise as to why. Especially for a fighter that has a high pressure style, 35 is an early decline than a pure boxer like Hopkins or Mayweather who had a little more longevity because their bodies fight differently and have lower output. Look at Chocolatito, he peaked sooner (Tyson, too, for that matter). Time is always against the pressure fighter, they simply don't have the longevity (Duran is an exception) of pure boxers.