Ok, here's how you can fix Garen's update right now.
Base stats HP per level reverted to 96 from 84.25.
Perseverance Regen at lvl 16 reverted to 2% of his maximum health from 1.6%.
Decisive Strike Silence duration reverted to 1.5/1.75/2/2.25/2.5 seconds from 1.5 seconds at all ranks.
Courage Now gives back Armor and Magic Resist based on your Bonus Armor and Magic Resist. 10/12.5/15/17.5/20% instead of 20% at all ranks.
Tenacity is back, being 10/15/20/25/30% from 30% at all ranks.
Judgement Make that slow on champions removed with ranks, 20/15/10/5/0% from 20% at all ranks.
Demacian Justice Increase the cooldown to 140/110/80 seconds
Increase the true damage from the passive to 1/2/3% of target's maximum health from 1% at all ranks.
Passive now only procs when the ultimate is available.
Basically, this rework just fucking killed all of Garen's strengths and made his weaknesses even more noticeable. Just give him these changes and the rework will be a success. Basically, Garen's late game is considerable stronger, while still being very kiteable. His laning is also nerfed to compensate, but is a still strong laner.