Simple Way to Fix Singed (His Passive)
Singed's passive should be changed to grant Tenacity based on Movement Speed.
I have a lot I would like to say on this, and can go into great detail on the subject, but I'll spare everyone. I also get that this will garner a lot of downvotes, because Singed. I'd be happy to answer any questions or comments people may have about this subject, as I have thought it through considerably.

Please understand, I know I am not good at league by any means (I am a Gold skilled player), I do however know the game intimately - I have played since Season 2, I watched every pro match of Season 3, and recorded statistics from those matches as research for a Game Design Textbook, but I'm just too old to be solid at competitive gaming; this however does not negatively effect my comprehension of their inner workings (those that can't do, teach/coach).
I have 1.3m Champion Mastery with Singed, I know the champion as well as almost anyone. I have also worked in the video game industry, have a degree in video game design, been a gamer for well over 30 years, and understand the inner workings when it comes to the creation and balance of these systems.
Singed is in a bad place right now, and if you disagree, you simply haven't played league this season, or are too jaded from seasons passed to recognize it. Most of the major Singed Streamers/Youtubers aren't playing, or are playing sparsely. Many have chimed in on the issue, but none have really offered a solution. I have one that will make it fun again.
If you want to hear a Challenger talk about the issue, there is an hour long video discussion: https://www.youtube.com/watch?v=6H0wq_IU8UQ