That’s a bit drastic IMHO. By default pipewire and pipewire-pulse are socket activated. I don’t normally bother with “Login” and “Logout” sounds, but I just tested this on Plasma 6 (openSUSE Slowroll) and was able to reproduce the same “no login sound on first boot” issue when PipeWire was running purely in socket-activated mode. However, simply enabling the PipeWire user service was enough to fix it. In fact, either of the following appeared sufficient to ensure the audio stack was active early enough for the login sound to play reliably:
systemctl --user enable --now pipewire.service
systemctl --user enable --now pipewire-pulse.service
No other workarounds required.