Adding to that that you can also easily make a separate WiFi network (tied to a vlan even) for IoT. OpenWRT makes this very easy.

It really depends how you define reliability. SD cards are physically nigh indestructible, but can show failure when overwritten often. Hence for one off backups it’s actually a good alternative. It will start showing problems when used as a medium that often writes and overwrites the same data often.

I would recommend backups on SD cards in an A/B fashion when you want to give a backup to someone else to store safely.

Consider running HA in a light weight systemd-nspawn container with minimal debian. No docker, only install the repositories you need. HACS if needed. Run your own database on the side somewhere and let HA use it.

By itself HA is fairly lightweight already.