Seb I'm not familiar with systemd boot, but I do have a couple scripts that disable and enable my login manager (lightdm) when I want to start sway from tty.
To disable:
systemctl set-default multi-user.target
systemctl disable lightdm
systemctl enable getty@tty1
To enable:
systemctl set-default graphical.target
systemctl enable lightdm
systemctl disable getty@tty1
Note: I run all of the above with sudo (not sure if necessary), and for good measure you may also need to add a 4th line for enable/disable getty@tty2
These steps should be easy to reverse if they don't work for you, but obviously proceed with caution.
