My estimation may be biased because I am Chinese, 2 years sounds like a more reasonably good figure, which is still a lot better then the 5 years Moser claims. Also there must exist at least one language genius who can do it in 6 month :)
Indeed as you say the Chinese language is hard at the start and gets easier. In my case when I moved to Australia I forgot a lot of my Chinese even after 1 year of not reading. 4 years later I could barely read, over the holidays I was forced to study Chinese, I did nothing but read a novel, some 10 pages a day which initially made next to no sense and took almost the whole day. But after two weeks of continuous reading, I could understand a lot more, and was reading much much faster(managed to finish a 400 page book). The trick to learning to read Chinese is to get going and not stop, and skip most of what you can't understand, and gradually you will pick it up.
I would also add that if you're not seriously committed to learning Chinese, why bother? Your progress would be so painstakingly slow it would seem you're forgetting as much as you learn - I'm trying to say don't do what Moser is claiming, tackle Chinese with less than 100% with slow progress and find out it is hard after 5 years.
It is also my view that much of the difficulty is a inherently negative mental illusion that the language is hard, and that also hinders learning. If people learned Chinese as if it were playing their favorite game, instead of something inherently dry and boring (which is another argument) this will speed up the learning process.