WAR is a good metric but the older the player, the less confident I am in it, especially someone like Brock who is punished defensively. Where we have StatCast and lots of reliable defensive metrics today, using old, less reliable, defensive data to evaluate a player's worth is pretty shaky.
Offensively, though, I think WAR is pretty reliable for players of all eras. And it does a good job of contextualizing things baseball insiders were just wrong about in the past, like stolen bases. Lou Brock racked up a ton of steals but he wasn't a great base stealer and is rightfully punished for it by WAR. And while Brock didn't hit an "empty" .300, he didn't bring a whole lot to the table beyond batting average. His discipline was fine but not great. His power was mediocre.
Brock's stolen base success rate: 75.3%. It's fine. Not great.
Whereas if you compare that to someone like Rickey Henderson: 80.7% success rate. And Henderson had 500 more steals than Brock. That's a ton of accumulated value.