Cards gave up pretty much nothing.
Carson Kelly has been tuted as their catcher of the future, until he actually plays in MLB and doesn't look like a catcher of the future.
Weaver has some promise, but they could certainly afford to give him up.
They also gave up a minor league IF I admittedly know little about, and one of their free extra draft picks that they get each year to help a team that "only draws 3 million" try to stay competitive.
Respectfully disagree. Let's start with goldy. He's 31 and only under contract for 2019. So, starting there he's not a huge value for AZ. I mean this is effectively a july trade in december. Great hitter, great defender. Not questioning that one bit. But the fact they only get him for 2019 is a big deal. Makes them better for 2019 sure but this is a team the last 3 years that's gone 86-76, 83-79 and 88-74. A 5 win player isn't enough for them to be a sudden favorite. They have a lot of work to do.
As for what they are giving up, let's start with Kelly. You're talking about a very good defender(60 arm 65 field) who has hit as a C(.269/.378/.395 for a 107 wRC+ at AAA). To put this into some context, as a 21 year old in AA he hit .287/.338/.403(115 wRC+). As a 23 year old JT Realmuto hit .299/.369/.461 with a 132 wRC+). We've seen the names thrown around in terms of trades for Realmuto. If you want to argue he's a slightly better hitter that's likely fair but overall the potential between the two is similar. And as that pertains to the cardinals, Yady isn't getting any younger. They do have Andrew Knizner who is ok but he's no where near the defender Kelly is and his bat while good from an avg stand point, doesn't have much pop. I'd compare him to Caratini but maybe a tick or two better as like Caratini he moved from SS -> 3B - C.
As for Weaver, hard to say on him. I mean you basically summed it up there's promise but at 24 you're not entirely sure if he meets it.
As for Andy young, he's more than just a thrown in. Fangraphs has him as a 40. He's a pretty good hitting likely 2B or UTIL. they have him at 50 hit 55 power which is more than you need to start and he's probably a below average 2B defender. He's not a huge ceiling prospect but I would actually consider him a prospect not bench filler or org filler.
And on top of that the cards also are giving up pick which is kind of a big deal. I think the dbacks made it out pretty damn well here given goldy only has one year of control. Kelly can be a starter at C. Weaver at worst is a mid rotation starter with some promise. Young might be a second tier starting 2B or a good UITL. And they get a draft pick. The cards get better but I think there's still a 4-5 win gap between the cubs/brewers and them.