Some data on Legion's performance since the Oni update
We've got enough data since the Oni release to make some comments on Legion's performance after the speed update.
For all platforms, all maps and all ranks, from Nov 2 2019 to Dec 2 2019, the Legion's average killrate was 61.99%, ranking him 12/17 in killrate. For reference, Nurse is at the bottom with 43.9% and The Nightmare is at the top with 70.83%.
In the same period but just looking at ranks 1-4, Legion is ranked 13/17 for kill rate. It's still Nurse at the bottom and Nightmare at the top.
If I switch to all platforms, all maps and all ranks from Dec 3 to Dec 19 (The Oni released on Dec 3), Legion's killrate is 62.5%, but that ranks them at 10/18 for killrate.
Just looking at ranks 1-4, the killrate is 71.2%, ranked at 12/18.
These are not massive changes, but they are noticable in a statistical sense given the sample size in terms of number of games played. We can conclude that the Deep Wound change (running stops the timer instead of TR) combined with the speed change (restored vault speeds and 5.0 m/s -> 5.2 m/s Frenzy run speed) were a net buff to Legion, both in terms of raw kill efficiency and in relation to the other Killers.
EDIT: Typo. It's out of 17 Killers the first month, then out of 18 after the Oni release. Apologies.