>Windows Vista and newer launch a more substantial version of the OS with the graphics system and Win32 services running, but they never intermix versions.
And yet, you can use the Windows 11 installer to install Windows 7 and have it be significantly faster because of that.
Windows Vista introduced a wim-based method of installing where it effectively unpacks a whole prebaked installation image onto the hard disk. It is the X:\Sources\install.wim file on the install DVD.
I'm not surprised that you can mix up versions by modifying your installation image, since the installation method hasn't changed since Vista. As Microsoft ships them, however, you boot Windows 11 to install Windows 11. :)
That's as much just the mid-Windows 10 era shift from the Windows installer installing Windows "one file copy at time" to shipping virtual hard disk images and installing the whole thing like (but not exactly as) a container overlay.
And yet, you can use the Windows 11 installer to install Windows 7 and have it be significantly faster because of that.