Without copyright YouTube could pay nothing for old movies because copyright doesn’t exist and they or someone else would upload any ‘exclusive’ content.

Now YouTube itself might volunteer to pay something to actually get new content because that’s in its own self interest. But that’s going to be at roughly current levels rather than an extra “blockbuster” rate because again any website could trivially have the top 10,000 videos on YouTube so they can’t gatekeep the content behind a paywall etc.