That argument is true for the finished products. Serie A have not bought world class players in their prime in past few years. However, De Ligt does not fall in that category yet.
Serie A doesn't buy hot young talents. It's very rare and only Pogba comes to my mind. Roma made some moves and those kids will be sold (and guess where... either England or Spain) surely but they weren't a huge name back then so they didn't attract top clubs. De Ligt is not a WC player he's one of the best young players in the world which instantly means top EPL and La Liga clubs will bid and provide him a starting spot too. His price will be insane, unlike all other talented kids that Serie A buys. When you see Serie A buy top players it's usually only Roma that does that. Inter and Milan are buying more finished products.
When was the last time we bought a young player which we paid a lot of money and offering him a starting spot? We bought Pogba for peanuts and he started playing slowly. All other players that we bought were either in the best age or fading stars that were revived. It's was literally one Dybala and IMO it's totally different when a player already plays in Serie A. We've got pawns on them more easily.
De Ligt is not even 20yo and he will cost over 50mln. IMO chances of us getting him are close to 0.
And I'm still thinking how many young players (<21yo) we bought for big bucks (>50mln). And yes, there are many top talents that can we bought for less, that doesn't mean they are worse players. But what I'm trying to say is... Juve and Serie A generally aren't the place for such type of players.