I Have been coming across a lot of decks that have over 150 cards in the deck and usually surpass the 200 card deck count on MTG Arena.

These games are never fun due to long drawn out games and for people that enjoy playing Mill decks the Mill deck will lose by default because the card value of milling is well balanced to achieve success when the decks have a quarter of a thousand cards in the library. Second; There are several answers in the game to either win the game due to not having cards in the library and ways to shuffle your graveyard back into your library.

Second this seems to be a direct tactic to "copout" to not have to get frustrated with the dynamics of playing against a Mill deck. It makes for the games to be no longer fun and put at an disadvantage for other decks that have sixty card deck size with games being drawn out as iterated before.

It can give the player with a maxed out deck with many answers such as board wipes taking up a third of the deck and perhaps the same could be said about counter spells. It is not fun if someone is board wiping the field or constantly playing counter the spell game for an entire match.

I believe limiting players to a maximum size of perhaps 80 card deck list would be much healthier on arena.