I've got to agree that he's in that somewhat bad spot where he's pretty much only usable in a case when you have a PhD at playing him, and anyone who isn't Marin is strictly forbidden from even clicking on his champion page.
Honestly, after the Juggernaut fiasco blown over, he was still playable and had his niche, which doesn't change the fact that the patch 5.16 was way too big of a hit to him, not only did top lane meta shifted purely towards Rumble counters but also he himself got nerfed quite heavily. Yea sure, he was a highly contested pick in LCS (was, until 5.16 and finals, until then he was barely even considered worth playing), but then, when you see that pretty much every single balance change made to Rumble was influenced by LCS, you've gotta ask yourself a question, who was this champion made for again? Was he like an order given by five people to have some champion that they can occasionally play competetively from time to time but something went wrong in Riot HQ and they accidentally released him onto live servers and ever since tried to keep his pick rate as low as possible?
And then there's this whole circlejerk around Rumble where apperantly he's like the most overpowered champion in the entire game that has also caused the most balance problems and is in general even worse than the meta top dogs of any season no matter what would happen, except that barely anyone even knows how to play him properly and his pick rate (again, aside from LCS) barely ever exceeded 3~4%, even at the time where he had 58,5% win rate back in season 3. And honestly, is he really that problematic? Sure, he's a strong lane bully, has quite high damage numbers and can control fights well, but that's literally all there is, and even his damage is highly conditional since it requires Rumble's enemies to constantly stay within two specified zones (which can be farily easily walked out of), he doesn't really have any mobillity and his only means of defense just outright sucks making punishing his mistakes fairly easy, his short cooldowns combined with heat mechanic do give him upperhand, but then, if you never forced him to overheat (which is one of his major weakpoints) then isn't that a sign of you just playing wrong?
Say what you want, but over the course of seasons 4 and 5, he was actually fairly balanced champion with a well defined role, and being a considerable pick in many teamcomps and the patches through 5.16-5.24 are just a series of unfortunate events that had way too big of an impact. I'm hoping that the upcoming mage patch will actually benefit him more than +30 ap when at full build, as it was with patch 5.13...