An avenger is an awesome unit that has been overshadowed by newer features unfortunately.
The avenger is a base game unit and as such is balanced to fight a human fleet that does not have any of the fancy toys the players get these days.
Last time I fought the avenger with none of the fancy toys enabled (we are talking months ago), I had to neuter the AI homeworld, rebuild my fleet, including all my turrets, in the adjacent system as a road block. I then destroyed the AI home command and the avenger proceeded to blow through my entire cap of both mobile fleet ships and turrets.
Fortunately it is slow, I was able to rebuild a significant chunk of my fleet and destroyed it at my second roadblock system which was adjacent to my own homeworld.
I want to say make spawning multiple avengers possible depending on what options are enabled but I think leaving the avenger as a base game unit and realizing that is going to make it irrelevant against the fallen spire or golems is the way to go.
D.