Good to know there's some algorithms behind the scenes. I thought I was losing my mind constantly playing mirror decks. I'll probably jump into ranked play. As it stands my causal games come down to whoever gets the better opening hand (which is true for all card games - but with the similar decks it feels worse)
The mulligan helps with that, and once you learn decks better you'll gain experience at knowing when to mulligan.
For what it's worth, the "better opening hand" or "who goes first" thing is still an issue in best-of-1 modes in general. The classic Magic style that's called "traditional" in Arena is best-of-3. A few things happen in best-of-3:
1. You have a "sideboard" of 15 cards. Between each game in your best-of-3 series, both players can switch cards out of that sideboard and into their deck. These are situational cards which are great against some decks, but not needed against others.
2. Because you are playing 3 games, luck of the draw should matter a little less, and overall you should have a better chance of winning. In terms of daily win bonuses, winning 2/3 games in a best-of-3 series still gives you 2 "wins".
3. Here's something you probably don't care about yet: As far as I know, the mana fixer is turned off in best-of-3 (I -think- it's still turned on in ranked best-of-1 but I'm not 100% sure). If you didn't know there was a mana fixer, yes, in best-of-1 play the system simulates two opening hands behind the scenes and is "biased" towards giving you the one that more accurately reflects your deck's ratio of lands.
If you have any questions please feel free to ask! I came from Hearthstone and things are pretty complicated in Magic sometimes.