I get what you are saying and some batsmen are great till someone finds a weakness and then they can't score a run after that. Ganguly is a good example I feel, who had a great start and quickly became one of the best ODI players in the world, till he was found wanting against short pitch bowling, and Shoaib Akhtar was one of those to trouble him the most. After than his stats really fell down. He still made a career after that, but he was nowhere near the same player in the second half of his career.
However in these days, there is so much analysis, that its hard for a player to hide. If he has a weakness everyone will be at him like hawk very quickly, and he will be found out. Williamson has been around long enough and played against the best there is. He is a solid player.