From the Homestead (update 13) patch notes we have:

Adjusted the distribution of Maelstrom weapons obtained from the Maelstrom Arena via the Leaderboards and drops.

• Previously, this was divided evenly by weapon category (Destruction Staff, Two Hand, etc). Now, it is based on the individual item type (Dagger, One Handed Sword, etc), and all damage weapons within the item type have an equal probability to drop.
• In addition, when a Dual Wield weapon is awarded, you will receive two Dual Wield weapons.
• We also slightly reduced the drop chance for Healing Staves, Bows, and One Hand and Shields.

Just some details on the current drop rate and what we can guess will be the new one based on the above patch notes. The chances in the following table are "Old / New" values:

• Restoration Staff = 16.7% / 8.3%
• Inferno Staff = 5.6% / 8.3%
• Ice Staff = 5.6% / 8.3%
• Shock Staff = 5.6% / 8.3%
• Sword + Shield = 8.3% / 8.3%
• Mace + Shield = 8.3% / 8.3%
• Bow = 16.7% / 8.3%
• Dagger = 8.3% / 16.7%
• Axe = 8.3% / 16.7%
• 2H Sword = 5.6% / 8.3%
• 2H Mace = 5.6% / 8.3%
• 2H Axe = 5.6% / 8.3%

The current/old drop rate is pretty well understood....each type of weapon (Destruction, Restoration, Bow, 1H+Shield, DW, 2H) has a 1 in 6 (16.7%) chance of dropping with weapons within each class having an equal chance. This results in some weapons like Restoration Staff and Bows to drop much more frequently than specific desired items (like an Inferno Staff).

Guessing at exactly what the patch notes mean...each of the 12 weapons now has a 1 in 12 (8.3%) chance of dropping. This matches the note that Restoration Staff and Bows have a reduced drop chance although it looks like 1H+Shield has the same drop rate so either this assumption or the patch notes are not entirely correct.

Also note that the 2 DW weapons (Dagger + Axe) have doubled chances in the above table making them the most common drop overall. Which is good as a stamina build will need 2 sharpened drops so anything to reduce the farm time is appreciated. The chance to drop an Inferno Staff is also increased by 50%.