Not necessarily disagreeing with a lot of what you're saying, but I don't really think it's true to claim that people didn't know how good his defense was. He's generally regarded as one of, if not the best defensive outfielder of all time. This is well evidenced by him winning 10 consecutive GGs, which corresponds with practically the entirety of his prime/years as an elite player before his precipitous drop-off in his 30s.
The argument of course, is that people didn't, and to a certain extent still probably don't, value his defense as highly as it should(?) have been. You're gonna have a hard time convincing most people, even today, that a 160 wRC+ DH-only - or worse, brutal defender like a lot of the sluggers of the 90s in a no-DH league were - monster bat is as equally valuable as a 115 wRC+ defensive superstar even in a premium defensive position like CF, SS or C.
For god's sake, the Braves even experimented with putting Chipper Jones in the outfield from 2002-04 since it probably didn't even matter how brutal he was if Andruw would mostly cover for his range. They knew how good his defense was.
I agree fWAR allows us to retrospectively give him some of the credit he deserves, and this may ultimately result in a HOF induction that one may not have thought about during his playing days, but that's not to say that people didn't know just how good he was at defense, relative to his peers, even at the time.