Your entire attitude in your post is saying "Wah I lost, when r Rumble nerfs, GIVE RUMBLE NERFS OR I QUIT". That is why I'll speak plainly and clearly to you.
I don't have to watch it. I just have to look at the match to see how little you actually know about the game.
A)You rushed Seraphs....as teemo. NEVER do that. It is a bad item for teemo.
B)You had 0 extra mr. Teemo has a base mr of 30. You didn't even take mr runes. Rumble rushes magic pen, so after his 33 magic pen, you essentially had negative mr.
C) He had boots before you did. We can see when items were bought, did you know that? He had base boots at 4 min, and upgraded boots at 9 min. You had base boots at 3 min, and upgraded boots at 11. So just from that, we know you don't have an accurate remembrance of what happened.
D) https://leagueoflegends.fandom.com/wiki/Rumble has all the information on his abilities. His q has a 10/9/8/7/6 second cooldown, and is active for 3 of those seconds. He also does 50% more damage if his heat is above 50 (the halfway point)
Essentially, if you itemized better, you wouldn't have this problem.
And to talk about how you're just calling for nerfs. I quote :
Is this seriously something RIOT's balance team let make it into the game, or did someone figure out how to use cheat programs in league? Frankly if it's the first one, I'm out, uninstalling, straw that broke the camel's back etc
That is just you complaining about a middle ground winrate champ. He isn't really good right now, and honestly if he was good he would be played in Worlds, since he has an amazing teamfight ult (as he has been in past years)
If it IS legitimately just that he has this much abusively broken damage, do we at least have an ETA on the incoming Rumble nerfs?
He doesn't need nerfs. Teemo will probably be getting nerfed before Rumble is, and that is who you played. Teemo actually has a 57% winrate against Rumble.
YOU GOT OUTPLAYED. Learn from it. Buy magic resistance, AND take magic resistance runes instead of bonus health (especially since its 15 bonus health at lv 1, not really going to help you as much as the 6 magic resistance. If you had taken that instead, you would still be positive when Rumble buys his 2 magic pen items instead of negative)
And above all else ACTUALLY TRY TO PLAY AS RUMBLE BEFORE YOU COMPLAIN. Coming to the boards and whining that he "does too much damage, and if he wasn't cheating then I quit the game" does nothing to help you. It just gives anyone who looks a reason to laugh at you. If you want to learn how to play against a champion, play as that champion. Learn what they do.