Truthfully, I don't know what the secret sauce is. In my experience: system d boot is very simple and allows us to hook directly into the bootloader without any fuss. GRUB seems to be an operating system of its own and windows knows how to hook into it if you will.
Yeah, I've been using systemd-boot for over 6 months, close to a year, and I've never had issues with Windows. And I've been dualbooting a lot. Multiple times, using different windows editions, like AtlasOS, or Windows after Winutil, and my sytem has never broken because of Windows and boatloader shenanigans. And to top it all off, in all of these instances, I had Windows installed AFTER Linux, and the only tbing I had to fix after install is to change the boot order so Systemd-boot takes priority.