Believing all of it happened is normigroid, believing none of it happened is also normigroid.
There wasn't a better way to kill people en masse, actually. They already had the building that could be modified into a gas chamber (all they did was chip holes in the roof) and when they realized they couldn't send all the Hungarian Jews east like they planned, they had to get rid of them somehow.
Keep in mind, they brought in over 800k on trains and suddenly couldn't deport them as planned. What would you have done?