I mean, you're asking for indisputable metrics on a 23-year-old right fielder that is pretty much universally held to have generational power. Potential is a massive portion of his value. He's got 100+ HR before his age 24 season and I'm not sure I've ever seen someone question his potential so seriously before I rose the point on this board. It's natural to over-value your own system and devalue other team's stars, but come on.
Again, I'm not saying Stanton is not a legit All-Star. He's just not yet proven himself to be one of the elite players of the game. If you're going to trade your most valuable prospects, you better be sure that what you're getting in return is a great player—not a really good player who, if he overcomes the injury bug, cuts way down on his strikeouts and improves his defense, will become a great player.