I worked on the AVC team and built the original SCK Instruments plugin for performance monitoring. I'm assuming you aren't talking about ring-0 (which is where the performance hit occurs). That said, if you want your users to be able to minimize/maximize any "watched" window, ScreenCaptureKit is a non-starter. The OBS team has been asking Apple to remove that restriction for years.

Here's a more real-world scenario [0] where Seymour has to handle more than a single window. I can cycle through the entire z-order at 60 fps while capturing all of the content windows. In fact, Seymore can display the contents of minimized windows, which the content server doesn't even support natively. BTW, this quick demo was done using a debug build. The release build can run at < 4% cpu utilization with a dozen windows active and has full multi-monitor and multi-space support. Also, remember that SCK pays no attention to windows that are hidden; something that Seymour has to do constantly.

Here's something else you can't do with SCK: picture-in-picture windows [1] that can exist even when the source window is hidden. This is super helpful when watching builds or app logs on larger monitors. No more command+tabbing to babysit things.

[0]: https://imgur.com/a/cfgrD0y

[1]: https://imgur.com/a/jiR3GQ0