I can tell you the joke doesn't stand scrutiny!!!
It starts as early as ep #4!! Dr. Harlan, a man Mark considers like a father, is killed in "The Space Serpent".
There is one of my favorite pieces of dialogue the entire series in this ep - Mark tells Debbie that revenge never helped anyone. Jason fires the missile while we watch the Phoenix engage the serpent. This is a perfect example of how the Sandy Frank Productions editing went a long way for the better!

In Gatch, Ken slaps the crap out of the daughter. While GoS didn't show the slap, Ace wasn't real nice to the daughter either and made her press the red button. But I digress and that's for another conversation.
Another example is Lucy from "Race Against Disaster" - she ran through a wall after revealing herself as a robot! This is the ep most of us want to disembowel Zark.
More (thanks to Jason's AWESOME Battle webpage!) examples include Diane and Orin in "Victims of the Hawk". Again, Zark gives his two cents and I find myself wanting to choke him!
Professor Wilde sacrifices himself to save his granddaughter and G-Force in "The Perilous Pleasure Cruise". Dr. Strecker kills himself in the self-destruction of "The Space Spider". Again, a cool scene is when Princess loses her bracelet and Mark and Jason cover her with their wings to prevent Strecker from taking her picture!
Zeno dies in "The Giant Gila Monster" after Mark blows up the portal that was his only escape. Zeno jumps onto the mech, takes it over and makes it explode.
There's others too. Akkadan is killed in his last fight with the "The Charioteers of Changu" and Uncle Ajeeb (we see his skeleton!) was killed by Zoltar and his men in "Demons of the Desert".
I know I didn't get everybody, but we see more than you would think!
And actually it begins as early as ep #2 when Okto is killed after he takes the Terrapin's head and tries to destroy the Phoenix after "The Rescue of the Astronauts"!!