There's really very little one can do to be "toxic" in mtg arena, outside playing a control deck, which is clearly part of the game or they'd stop making counterspells. "Arena is toxic" means "I lost".
It's funny how biased against "playing to win" hacker news frequently is. On one article you'll have dozens of people arguing that a company is legally allowed to hurt people and therefor they should, then the next comment section everyone is complaining about losing in a game of mtg.
Only toxicity possible is roping which definitely gets annoying. WOTC should crack down on serial ropers. They certainly have the stats to be able to do this.