shuffler
The shuffler is horrible. I have played paper for 25+ years and never had the issues I get with Arena. I have a deck with 12 pseudo dual lands and 4 of each of 2 different basic lands. I often draw 2 of the same basic land followed by a mulligan giving me 2 of the other basic land. no other lands on either account. Sometimes I will draw 3 of the same basic lands with no others. Similar things happen with spells. I will have 2 of a specific spell in the deck and draw both. After a mulligan, I may draw another 2 of the same spell, or 2 of a different spell of which I olnly have 2. In addition, it is very commonplace for me to draw mainly land when I need a spell, or only draw spells if I need a land. I have mulliganned down to one land with having the spells I need in my hand only to not draw a land on my next 5 turns (with land being at minimum 33% of the deck). My draws rarely match half the odds of when I should draw a card needed.
Secondary comment: my opponents tend to always have the exact card at all times to either slow down or stop my deck. Seems to be more prevalent with those who regularly spend actual money on the game.
Third comment: paying players seem to go first way more often than others. If this is in doubt, there are plenty of youtube videos that claim the same as well as delve further into my previous comments as well as other comments
on this site.