So I guess your question wasn't in good faith then, but just bait so you'd have an excuse to rant about things unrelated to my answer?
The security issue that Wayland helps solve has nothing to with systemd or logind, so I'll just ignore your tirade against them. If you don't want to use them, then good on you.
The issue is an inherent issue with the X11 protocol. It can be worked around, but it can't be fixed without something changing in the protocol on a fundamental level. The core premise that any client can be trusted unquestionably is broken and was broken the second browsers began running JavaScript. Not to mention all the other times most modern computers run opaque code of uncertain origins.
Keeping it simple is definitely a great basis to build a secure system upon, it just can't stand alone because of reasons like the above.