Here's how I think a better version of Star Castle could have been attempted from back in the 80s:
The Qotile, instead of just moving up and down, probably tries to move towards your horizontal position. The speed increases as the levels go up.
Instead of the shields in Yars' Revenge, 3 columns of Circus Atari-like blocks. They move up and down, in opposite directions between the 3 layers. If a layer gets completely destroyed, it either gets renewed or the deeper layer replaces the "upper" layer.
The Qotile shoots a clear shot at the Yar (or probably just horizontal) if there's an opening in its shields. The shot could re-aim itself in higher levels.
The destroyer missile stays the same.
Unsure if the Zorlon cannon should still be used or just have the normal shot for destroying the Qotile.
These are part of an Atari fangame for Windows I've been having, but I might not end up making it due to lack of interest.