On a municipal level, yes. They are basically their own town.
But not at all at a county, state, or federal level.
If the county shuts down, WDW shuts down.
If the state has a resort fee, WDW pays it. WDW also has to abide by all the state water management laws and can be told point blank, "No, you can't build there, that's protected waterways." WDW is lucky that Florida isn't as much as a stickler for inspection and approval of building codes and guest safety rules for all amusement parks. But if Florida wanted to be as restrictive as California, WDW would have to comply.
WDW has to pay all the Federal taxes: Income and the employer's portion of Social Security and has to abide by all the federal labor laws.
So, WDW does not have 'enormous governmental control.'