Its not a bias.
Here's the deal. Death of major characters should be earned, not just jumped to. It took TEN YEARS for Marvel to use the (possible) death of their main characters as an emotional crutch or story point. DC took 2 movies.
If DC went straight to Civil War in in phase one, people would have been just as irritated.
The other major issue is that people (fans at the very least) want their comics movies to resembled their source material. Every iteration of mainstream Superman in film and cartoon doesnt have him murder a dude and die within his first year of work. Its like when they reboot a show or movie wrong. DC/WB owns all their characters and stories outright. So unlike MCU who have to change things to dodge plot points they cant do, DC has no excuse when they make weird decisions that are detrimental to the characters or story.
The only reason it seems like people have a bias in favor of MArvel is because marvel has earned peoples trust, where as DC is just trying to force it.