Adrian Gonzalez .329/.386/.503 146 wRC+
Prince Fielder .273/.397/.487 138 wRC+
Clearly one is better then the other?
Let's start with the basics:
Prince Fielder is 29. He was a regular at 22 and hit 50 HR's with a 158 OPS+ at age 23. He has already posted 4 seasons with an oWAR greater than 5.
Adrian Gonzalez is 31. He didn't have a breakout season until he was 27. He has only posted 2 seasons with an oWAR greater than 5 (with one at 4.7).
In their careers, with Gonzalez with a 90 PA advantage (which is obviously small), Prince has him beat in oWAR (31 to 27), OPS+ (144 to 137), OBP (393 to 371) and RC (928 to 856) and wRC+ (142 to 133).
Gonzalez has a "prototype" career arc - regular at 24, peak 27-29, began decline at 30. His power is gone, he hit 18 HR last year and is on pace for 18 again. His walk rate has collapsed, 42 walks last year, on pace to hit 55 this year.... in his peak he was at 119 and 93. His only saving grace is that he has improved his K rate significantly. Even still, he is a .292 career hitter who's entire slash line is being propped up by career high .348 BABIP (career average is .325). He is developing into a BA driven, defensive 1B. At age 31. That is not a good path. Not to mention the turd he laid last season.
Fielder is an early developer (good). His power has been consistent through his career when you adjust for the ball park and league shift last year. He has always walked a ton and still walks a ton - He is coming off 2 consecutive seasons in which he walked more than he struck out. He is coming off back to back seasons with an oWAR of 5.5.
So no, there is no fucking similarity other than a 50 game sample size.
Adrian Gonzalez is a 31 year old 1B who is relying on line drives and defense for his value. Based on his last 880 plate appearances he is in a clear decline.
Prince Fielder is a 29 year old who takes a ton of walks and hits HR. Based on his last 900 plate appearances he is the same player he has been since he was 23 years old.