Updated 06/08/2019. The class has had quite a few changes since I originally made this post, so I figured I'd make some more suggestions. These are just trait and legend changes, no weapon changes.
Currently Mallyx lacks the sustain and reactiveness to be a competitive mid to close-range fighter. The biggest issue I see with the legend is that Pain Absorption has a cast time, making it unreliable and at times a liability when attempting to break a stun. I felt a leap finisher is warranted for Unyielding Anguish since dark auras are now a thing. The skill itself is already quite strong and although I have seen suggestions to give it an evade frame, I find that more fitting for Pain Absorption. Embrace the Darkness being instant cast opens it up for better trait synergy (such as Diabolic Inferno and Expose Defenses) as well as giving it better synergy with power builds as it could be timed for spike damage.
There are some very potent traits within the line, but it is currently too catered to Mallyx and is rather lackluster otherwise. These changes have been made in an attempt to diversify its use for both power and support builds, making it less of a niche traitline and diversifying core Revenant’s boon access. This would give Mallyx more competition as a viable secondary support legend for the core class.
These changes are aimed at making Ventari more reliable and self-sufficient in PvP/WvW without improving its numbers or PvE performance.
The recent changes to the traitline have introduced two stellar traits for self-sustain: Resilient Spirit and Unyielding Devotion. However, the orb mechanic is still very lackluster in its current state and encourages bad positioning for little reward. Simply put, they need to be made more functional. Additionally, removing regeneration access from the traitline was a big blow to builds that relied on Ventari--and not Glint--for regeneration access.
Jalis is a bit of a weird legend and one I'm a bit more stuck on, so the suggestions are a bit more minimal. Not too much to say here.
The rehaul to some of the Retribution traits was a huge step in the right direction. I don't think too much needs to be changed here.