I think the "amount" issue is kind of splitting hairs. If the goal is to use this to entice paper Magic players to try out Arena, the difference between 6 packs and 9 is negligible. You're not making any kind of meaningful deck out of either of those, even for just regular Play mode, so if this was supposed to be an intro to Arena, it's a bad one.

The difference between X random packs (even if it were more than 6) and an entry into a sealed or draft event is much bigger. That's something that puts people on a level playing field and doesn't require them to try to immediately build their own deck out of terrible garbage, and gives them a chance to see how the game plays and what it looks like, comparing it to the experience they just recently had playing sealed or drafts.

To me, they could have made this code be worth more packs than a sealed entry and it would have been a change that didn't make sense if the goal is to use it as a hook to attract more paper Magic players to try out Arena.

On the other hand, this actually seems like it might be a better deal for established Arena players. 6 packs with duplicate protection and progress toward wild cards seems like it's likely better than 9 packs but 6 of them don't have 5th-card protection and don't contribute to the wild track. Now granted, I doubt even many established players have all that big of an M20 collection on the first weekend, but it's still an interesting thought. I think I'd rather have the sealed entry than 6 packs, because I'm also decent at sealed and could potentially get some decent gem prizes out of it. But it's just interesting that this is a change to something that's arguably better or worse for an established player, but seems unquestionably much worse for a new or casual player.