The ladder system is a set of server specific leaderboards. It's mostly for bragging rights, but diamonds can also be earned for everyone on the server when a player completes a ladder task for the first time.
In patch 1.17.01 the "Ladders" tab was changed to be called "Wall of Legends", and now has a building in Ranhorn.
Server Firsts
The first player to complete a task on their server will have their name and avatar permanently displayed on the ladder rewards page under that task as a recognition of their accomplishment. The top 5 players will also be displayed on the log for it.
Leaderboards
The top 50 players on the server will be displayed for each ladder. The #1 ranked player for each leaderboard will have their name and avatar displayed on the main ladders page.
There's currently 6 different leaderboards to compete on:
Faction: Lightbearers
Faction: Maulers
Faction: Wilders
Faction: Graveborn
Campaign Stages
King's Tower
Faction Ladders
The rankings on the faction leaderboards are based on ascension levels of each players heroes. The higher the ascension, the more points a player will earn.
Duplicate heroes will not reward any points, only the highest ascension of that hero will count towards a players ladder points.