It’s been a long time - like, 25 years or more - since any of us actually watched Dave Winfield in his prime. It’d be interesting a find a lot of tape of him then and actually watch with a critical eye, and even then I don’t think such tape exists.
People are, quite naturally, remember Winfield for having an excellent arm. An outfielder throwing out a baserunner is one of the more memorable and spectacular things he does, but it’s also a very small part of an outfielder’s skill set. Much of what makes a good outfielder is not visible on TV because it’s comprised of things they never show you - the outfielder’s initial reaction time and the correctness of his initial break, and how true a path he takes to the ball’s landing point.
It’s quite possible Winfield was very physically gifted but just wasn’t good at getting a jump on the ball - maybe the numbers are wrong but it is interesting to note that they are consistently mediocre throughout his career, worsening as he ages, as you would expect. There’s no obvious illusion of context; his numbers are mediocre, and get terrible, everywhere he plays. He is mediocre in San Diego, gets bad in New York, and is abysmal in Anaheim.
It would be interesting to ask why Winfield is, allegedly, so unique among MLB fielders that the numbers are that far off on him. Every other guy who think was a great fielder is at least pretty good and everyone you expect to be awful is. I think it’s on the doubter to explain why Winfield is an exception. I stress that I can’t explain it - it’s just too long ago, and he was in his prime when I was in kindergarten.