There’s definitely some truth to this. The subconscious is programmed to recognize patterns, so it picks up when multiple elements conform to a unified theme, creating a sense of satisfaction for the guest even if they aren’t fully aware it’s happening.
However, conformance to a theme is only one aspect of a theme park and often needs to be weighed against other concerns. For example, I don’t think it’s always worth maintaining perfect thematic integrity at the expense of adding fun attractions. That doesn’t necessarily mean throwing the theme completely to the wayside, but rather stretching it a little to accommodate new things.
Of course, a moderation in all things including park operations and some things will be non diegetic, but what is presented and recent track record does not seem to be the case.