Yeah, certainly. That's why I said "not really" instead of an absolute statement, to leave room for cases like that (and I probably should've been more clear). But for the most part input speed isn't the bottleneck that people get stuck at indefinitely.
And it's also possible for this to change. With programming, for example, if you lose the use of a hand, you quickly find out typing speed is the new bottleneck.
I'm an extremely slow reader and that has been a major bottleneck in my life, it has slowed me down in everything I do and everything I've been interested in.
Bill Gates is rumored to read several books per weeks and fully understand and remember most details. That in itself isn't enough to have made him who he is, but I'm sure it helps. If I could get one thing from him that's what I'd pick, yes over money and programing abilities, reading slowly is that delibitating.