So I eventually need to devote a day to playing like 100 matches to be sure, but yeah; there's no way that Arena is completely random.
Worst offenders I've seen are:
* Playing Brawl and facing same enemy commander, if not same opponent twice in a row
*Casting Omen of the Hunt and immediately (after library has been "shuffled") saccing it to Scry 2 only for there to be two forests underneath in back to back games
*Miracle top decks which let opponent win (again in brawl)/miracle top deck that lets me win
*Opponent having every single card they needs to counter my deck while setting their combos up
Worst offenders are always in Brawl. the format should be akin to having a bag full of letters, randomly pulling out one each turn, and trying to make the best words possible. but, inevitably, for one player, the game is more like 1,2,3,4,5,6,7...etc
Games that are balanced, where both players get to utilize their decks are so rare, it's still fun even when losing. 9/10 one player, through any combination of land fucked/flood, miracle draws, mirror match or enemy having perfect opening hand, just gets steam rolled