While Magic: The Gathering's London Mulligan rule has been a breath of fresh air for the game's competitive play, it hasn't come without some serious drawbacks, some of which have become magnified by the way the game has progressed in its many formats since the modified rule was instituted. For those unfamiliar, the London Mulligan allows players to send hands back to the deck that they don't like, shuffling and then drawing a new seven card hand as many times as they like. For each time they do this prior to the game beginning, however, they must put one card back for each time they used the mulligan.
On the surface, Magic: The Gathering's London Mulligan rule has reduced the amount of games that players aren't able to participate in. Sculpting a hand out of repeated looks at the maximum number of opening cards makes having something that is functional much more likely. This, in turn, has allowed some strategies that might otherwise be a little too inconsistent to thrive or at least remain competitive. The London Mulligan is at it's most noticeable in Limited formats, such as Throne of Eldraine draft, where the relatively low power level of decks means losing a card or two to solidify mana development isn't as pronounced.
However, the most recent wave of Magic: The Gathering Standard bannings might have been at least partially caused by a more subtle effect - the London Mulligan rule. Recent bannings have almost universally focused on cards that were part of decks that were "too consistent." In essence, they were strategies that had a small number of incredibly powerful and synergistic effects that could realistically be easily found thanks to the London Mulligan rule. It doesn't matter if players are down one or two cards on their opponent when they're the one casting the more powerful cards, faster. Redundancy is a powerful tool in Magic: The Gathering because it helps remove some of the complexity in the game's deckbuilding decisions - and, as the world's most complex game, any ability to reduce the amount of brain power needed in a given moment is a huge burden off the shoulders of competitive players.
It's not that Oko, Thief of Crowns isn't an absurdly powerful card in Standard and deserved to be banned. It's more that the problem seems to go so much further beyond Oko that it's at least worth considering whether the London Mulligan rule comes at too high a cost for what it does. This is only exacerbated in formats like Modern, Legacy, and the newly created Pioneer format - most of the top decks in each of those vastly different playing fields are those that take advantage of the London Mulligan the most. When cards are extremely powerful, players need less of them to enact their gameplay and functionally win a game, which once again makes the London Mulligan a powerful tool.
Now that Magic: The Gathering has surged in popularity once more thanks to Magic Arena, it's also worth considering the fact that the London Mulligan - posited as a net benefit to viewership experience when it was introduced - is actually making games more dull. Players are able to enact their gameplan with startling consistency, and the result is that most games look nearly identical. The games become about which deck has an inherently better matchup all too often, and the scrappy wins - the ones where a player has to cobble together a Plan B because their deck isn't co-operating, coincidentally the most memorable ones from a viewership perspective - have become increasingly rare. As Magic Arena continues to become a focal point of the professional circuit in 2020, repetitive games could lead to a lot of viewers departing streams early.
The Magic: The Gathering London Mulligan rule isn't a bad one by any means, but it's also the most fundamentally game-changing rule that's been instituted in recent years. In games that are exciting precisely because of their variance, like Magic, a rule like the London Mulligan is actively resisting against what makes the card game so great. Hopefully, Wizards of the Coast looks long and hard at the Magic: The Gathering London Mulligan rule over the next few months because, if there are even more bans required in the near future, it's probably not just the very powerful cards that are warping formats around one or two highly consistent strategies.