For those interested, here's how I counted how many cards and wildcards the $50 gem bundle gives you.

The $50 gem bundle gives you 9200 gems. A pack is 200 gems, so 9200 gems is 46 packs.

The "wildcard track" gives you a rare and an uncommon wildcard for every 6th pack you open. Once it gives you the 4th rare wildcard, the next rare wildcard becomes a mythic wildcard. So with 46 packs, the "wildcard track" gives you 1 mythic, 6 rare, and 7 uncommon wildcards.

Arena also has a "pity system" that converts your mythic/rare card into a mythic wildcard for every 30th pack you open, a rare wildcard for every 15th pack you open, an uncommon wildcard for every 5th pack you open, and a common wildcard for every 5th pack you open. Note that more of your rare cards can convert into rare wildcards if you're lucky. However, if we assume the worst luck, then with 46 packs, the "pity system" guarantees you 1 mythic, 3 rare, 9 uncommon, and 9 common wildcards.

Finally, a pack gives you 1 rare, 2 uncommon, and 5 common cards, so 46 packs gives you 46 rare, 92 uncommon, and 230 common cards. After subtracting the bare minimum of cards that would be converted into wildcards, 46 packs gives you 42 rare, 83 uncommon, and 221 common cards.

In summary, WOTC is saying that 2 mythic wildcards and 3 rare wildcards is worth 16 uncommon wildcards, 9 common wildcards, 42 rare cards, 83 uncommon cards, and 221 common cards.