Your argument of "ease" is flawed. The fact is if people want to murder they will find a way. In the UK they banned guns, then knife crime want crazy. They banned knives, now they stab each other with screwdrivers. Then they FUCKING BANNED SCREWDRIVERS, or rather walking around with them on the street without just cause.
Your premise is flawed.
Homicide rate in the UK (guns, knives, screwdrivers, whatever) is ~80% lower than in the US so I wouldn't describe it as "crazy".
If it was easier to kill it via other means why would all these mass shooters choose the harder way via guns? You're not making any sense. You bring up an arson example from last year and California wildfires... there is a mass shooting nearly every day.
https://www.usatoday.com/story/news/nation/2018/11/08/thousand-oaks-california-bar-shooting-307th-mass-shooting/1928574002/