1. First of all, you could print proxies when playing with friends to try out card.
2. You could buy individual cards from other players or your local game shop.
3. You could sell your cards.
The previous iteration (MTGA) had both 2 and 3 as part of the game. What's more, they would let you "cash out" your digital cards for physical cards.
You were not required to get cards by opening packs (which I agree is the ancestor of digital loot boxes). But Arena got rid of any way of getting cards outside of "lootboxes" because they want to get as much money out of your as possible, not because it's better for the game.
I think it's high time that the first sale doctrine (https://en.wikipedia.org/wiki/First-sale_doctrine) be applied to digital goods.
And you can buy individual cards in arena. You can buy wildcards in the store and redeem them for any card of the corresponding rarity. They’re stupid overpriced in many cases but you can’t say it’s not possible.
I was not aware that they introduce that. I gave up on it a while ago.
But wow, those prices! So they kinda addressed the purchasing individual cards, though the trading aspect of the trading card game is still conspicuously missing.
The hate against arena isn't due to lack of polish or it not working well, it's about what it's trying to do. It's not about collecting or trading cards anymore it's about opening as many loot boxes (packs) as possible.
MTGA let you purchase specific cards, Arena does not and likely never will. That isn't an oversight, that's a conscious choice to get people to spend money on buying more digital packs. That's a big reason it gets hate.