... and all the third-party software that was compiled for older versions of OpenBSD is now also broken by default. The problem is that this approach only work

... and all the third-party software that was compiled for older versions of OpenBSD is now also broken by default. The problem is that this approach only works if it is really a self-contained system. But OpenBSD isn't: it's a basis to run software, potentially third-party software. It's can't be a closed Universe and still be useful at the same time.