Please do, I'd love to hear your arguement against Stoneplate + Flash + ult on the ADC in a team fight, and explain to me why that nearly instantaneous combo can't be pulled off ever, as that's literally what you're saying.
For starters neither of us have ever mentioned that the combo could never be pulled off. It does exist and has been used before and after the E changes. However it is very unreliable and circumstantial, this is the reason why he wasn't OP before E changes.
Meanwhile you've not addressed the original point, which is what exactly is your idea of counterplay against that high of a true damage burst, that I've shown through simple math, to be easily attainable even when behind in the game. Instead you'd rather attack me for being a casual player, when playing experience is not relevant in the slightest.
I did address it in simplest terms because I did not feel like writing about it. "CC and mobility" is everything you need to stop a slow moving tank with 0 mobility. That is also why I said experience would help in understanding his counter play because it's very evident. I'll go into depth about why your example is flawed. Also I did not attack you for being a casual player. I actually find it very insulting as you would imply that I am the type to disregard others based on experience. I merely said that through experience the counter play to Cho'Gath is really evident. I did not say "You're a casual scrub so you don't know what you're talking about". Furthermore if you searched me up you would realize that I'm a "casual" player as well. I never play ranked, and only get gold from placements for the Victorious skin.
I asked a question that you refuted by saying it's not possible to attain those numbers unless extremely fed. I showed you how easy it is to attain those numbers, and you dodge the question again.
Where did I say that Cho'Gath needs to be extremely fed in order to attain those numbers? I did not dodge your question I answered it in simplest terms "CC and mobility", basic mechanics that you learn with experience. I'll tell you how it works though.
I don't care if you play one game a week, or play nonstop practicing to play on SKT. If your flash is down, and Cho'gath does the combo I mentioned, you don't magically not take the damage because you play more games than I do.
And Cho'Gath doesn't magically bypass your teams peel, crowd control, and ignores the priority target's mobility or damage.
So first problem with your example is that your simple math is wrong. Cinderhulk doesn't increase total health by 20%, if it did tanks would actually be busted, it increases bonus health. So your calculations in theory would go like this:
(960 + 325) * 1.2 = 1542 bonus HP from items
( ( ( (1542 + 2000) * 1.6 ) - 2000 )* 0.1 ) + 650 = 1017 damage
Next Cho'Gath actually needs to have many circumstances line up in order for him to get onto a squishy. Those circumstances I brought up else where, but I won't repeat myself cause you already understand.
Now there's more problems with your case. A level 18 Cho'Gath with only 2 items is nearly impossible. Experience and gold work hand in hand and if Cho'Gath only had 2 items he wouldn't be level 18 but probably level 10 or 11. The amount of damage his ult deals decreases even further considering this.
1454 base health
(720 + 323) * 1.2 = 1252 bonus HP from items
( ( ( (1252 + 1454) * 1.6 ) - 1454) * 0.1) + 475 = 723
So it's less damage than what you got before. Now consider that Cho'Gath did not have any tools to get stacks with his R effectively, as mentioned in OP, we know that getting stacks past that would be difficult. Also he had unreliable damage if people bought magic resist against him, and would over time be beaten by other kinds of fighters. Also ignoring the fact that if Cho'Gath was behind, which is definitely possible because he was not as good as doing anything before E changes, his enemies would have an advantage over him.
So this is high damage but I've already explained in my other comment that it was too unreliable. Your example is flawed because you ignored too many circumstances that I speak of in the other comment and because your math is off.