Insights on Rumble
Rumble has been struggling for a long time now ever since the juggernaut patch and even some time before then. He loses in a lot of match ups, mostly against Riven, Irelia, Aatrox, and Trynd. After the juggernaut patch, he's been losing more easily against champs like Nautilus, Maokai, Garen, Darius, Tank Ekko, Tank Fizz, and anyone else who builds tank with undying grasp. He didn't receive amazing buffs with the juggernaut patch, nor is he getting buffed for the mage patch.
As a Diamond 1 Rumble main with almost 2k games on him, I've found that the only way to make it out of laning phase as Rumble versus any of the listed champs, is to just afk farm/avoid dueling until level 6 then TP gank another lane. Of course I've done the 1 v 1 dueling pre six where Rumble is strongest, the lead disappears soon after any of the listed champs hits level 6. His ult is very hard to balance since it's incredibly strong in teamfight but incredibly weak in 1 v 1 situations located in the middle of an open lane. I've suggested adding a stronger slow or small initial damage to the first target hit or widening the ult width just a bit, but none of that received any attention.
So instead of changing/buffing the ult maybe give his shield an extra boost to better play against juggernauts? Once above 50 heat, Rumble shield will give him the original base shield + a percentage of his (Bonus/total/%missing) health. Rumble builds into a lot of HP items just to make it so that juggernauts can't completely outduel him. I believe this buff will make him at least start on an even ground with juggernauts and dorans shield start will actually be better on him than the corruption potion start I've been using.
(Yes corruption is better than doran's shield for Rumble.)