MTGA has always been a cheaters paradise but now every mode is close to unplayable.
There is not a single mode where you can use standard decks without being matched against a hacker who just rigs the match.
For the record I like the concept of deck building. But it should be reserved for ranked and super competitive play, where it belongs, with all the butthurts who can't handle losing.
A "casual mode" would be handy where both players are limited to standard decks.

1. This is a card game - you never get beaten on skill, you get beaten by better cards.
2. Some of us enjoy Color Challenge. This is for smart people who actually want to use skill with some of the more basic cards. Logically, if I am playing color challenge the opponent should be playing color challenge also - and bound by the same deck rules. Single color, 60 card STANDARD deck vs single color, 60 card STANDARD deck. That's called a level playing field, try it.
3. There should not be cheese cards. They only exist for the people who are too stupid to learn actual strategies. Wizards of the Coast are under the delusion that "Magic is for everyone". It is NOT for everyone. It's for butthurt hacker cheats and noobs who can't play unless they have cheese cards. Those people account for 99% of the player base.
4. Decks for Starter deck duels simply don't work. These are supposed to be random cards but players are still clearly hacking the game. Not once but literally thousands of times I've seen this, in all modes. As soon as you get the upper hand or play a card that is even slightly advantageous, opponents will mysteriously draw the EXACT cards needed to combat whatever you do. It is painfully obvious they are using an open deck stacked full of cheese and can just play any card in their library.
5. Mana $crew. The game is programmed to prevent you playing certain cards. Example: if a card costs 5+ mana, the deck will find a way to never give you more than 4 mana. In other cases, you either get a hand full of lands and no creatures or creatures with no land to play them. Rigged.
6. Timewasters. The bane of existence. Play a land, then play a creature or spell - it's not hard. I have seen multiple players just sit there for 10 minutes without the timeout fuse appearing. There needs to be an INSTANT penalty for this. All turns should have a maximum 30 second timer no matter what. If you can't do what needs to be done in that time, you forfeit the turn.

The system needs a complete overhaul. Due to these issues the game is actually not fun anymore.