You might want to re-read what I said. There were two operative words: "most" and "convincingly."
Pointing to those few episodes in which a main character dies doesn't begin to contradict the concept of "most," which by the way indicates a third word that was also key in what I said: "jeopardy." People don't have to die to be endangered, or in order words to be put in jeopardy, and that takes us back to the "convincingly" part. I'm quite familiar with how completely unsuspenseful most instances in Trek of the main characters being jeopardized were, having, you know, seen them all, in most instances multiple times. Palicki sold the idea that she was getting beaten up, that she wasn't going to crack, and therefore that she was in danger. It was also a plot point that Kitan had taken a blast that really hurt her. The delivery of both of those easily beat, say, Picard's "Worf went down" in "The High Ground" in terms of creating a sense that main characters were actually at risk of harm. Sticking with "The High Ground" as just a random example, the bomb planted on the warp core took so long to explode that any sense of danger was completely sucked out of that scene, as it allowed Geordi to do whatever was necessary to get it off and out of there.
Putting main characters in jeopardy is just one type of drama, but it's an example of where The Orville is doing just fine so far.
