How does that work for pages whose exact appearance is a mix of "user created" (copyrighted by the users, not the site) and "algorithmically generated" (not copyrightable)?
I'm not entirely sure "a webpage's layout" is copyrightable either, but even if it is, the only way an ad is ever actually part of that is when the ads are in fixed locations on the layout.
And then there's the fact that the modified version the browser "makes" is only ever seen by the person using that computer.
So this argument against ad blockers is like saying that writing fanfic is illegal, even you don't even post it anywhere.
If they want people to see the ads, they need to get rid of every ad that has any capacity to put things on your computer in any way other than displaying the ad on your screen. Unwanted trackers should be illegal, and ads that include malware should lead to jail time for the offenders.
Autoplaying video ads on non-video pages should also be banned.
Along with whatever is going on with Wikia's current layout.