I thought ffortnight disables this feature to improve performance
You don't understand implications.
1. Disabling it for games that have enabled it already won't give you performance boost. Why? Because devs already tested that spending 100 MB on recording didn't impact performance.
2. But if devs decided to disable that before release of game, then that means this 100 MB is important for them and without them game could have memory bottleneck and impact performance.
So it's not like disabling it will give you visible performance boost in every game.
And it doesn't change the fact that games for allocating this memory don't use any dedicated SDK functions. Just simple malloc() or new(). So you can't do that without IPS patch or skyline plugin on per game basis.