Champion select extremely laggy

Ever since the updated client came out, champion select has been extremely laggy, sometimes even preventing anything from being done. For example, in ARAM, where you can reroll and trade champions, I might use both of my rerolls and trade twice and end up not being able to switch my masteries or runes at all because of how nothing loads quickly, if at all.

The lagginess is a huge detriment to the client as well as to gameplay, because not being able to fix all of your settings in champion select means that you might not be equipped for the game to come, thereby doing poorly and bringing your team down despite your best efforts.

Using the legacy client is going to be removed completely in the near future, which means that it will no longer be an option.