There have been a lot of cases in the past where Tesla says one thing, then later it turns out it's something completely different.
I think we're all just trying to get more info. So far you're the first person whom Tesla has mentioned this to. And this would be a big hit to EVERY Tesla driver, so it's a big deal.
The Tesloop taxi driver who drove the Tesla for 200k miles and supercharged daily didn't mention any sort of slowdown. And I'm sure he'd notice. There are multiple drivers on TMC who put over 100k miles on their cars, a lot of them supercharged, who never noticed a slowdown.
So I can understand people's skepticism. I think everyone believes that you were told this information. People are going to question whether the information is valid or not.
"Information"... I had someone on the 800 number tell me that using Ludicrous mode even once voids your warranty. It's not easy to get "information" from Tesla.