WARNING: Assumptions built on assumptions ahead.
When looking at market share, "unique visitors" is a very important number, and the tables in the report don't tell us that. But we can probably assume that visitors to WDW turn the turnstiles at the MK more times during a week-long vacation than they do at AK. In fact, AK may be a "once per vacation" park. So using that number, WDW may be drawing around 10.2 million people per year. Those 10 million people might be going to the MK on average 1.8 times per vacation, and AK once per vacation, accounting for the turnstile differences between the parks. And perhaps US is a "once per vacation" park as well, and it is drawing around 7 million per year. So in comparing unique visitors, maybe WDW is drawing around 10 million to US's 7 million. WDW wins, but the difference might not be as great as it seems.
But also, many (most?) of the people at one company's park are the same people who go to the other company's park. This isn't like Coke vs. Pepsi at the grocery store. A small percentage of people might buy a 2 liter bottle of Coke and a 2 liter bottle of Pepsi during the same store visit. But most choose one or the other. If 10 million people buy Coke and 7 million people buy Pepsi, that means there are probably close to 17 million cola buyers. But that is not the way Central Florida works. Since there is a lot of cross-over, if US grows in numbers, then WDW probably does too. And vice versa. A clear case of a rising tide raising all boats.