FAs definitely should not be given the power to divert a flight for things like this.
FAs are safety officials. Their customer service duties are secondary to that role. There are countless stories of great FAs saving lives and sadly the reverse. FAs aren't the ones who decide to divert, the captain is. Though the captain is going to rely entirely on what they hear from the FAs. And they need to have that authority to do that for instances where an emergency landing or diversion is indeed necessary. If the captain had to verify each case and couldn't rely on the FAs, that could be potentially catastrophic.
The issue is, like Dan said, that they appear not to be trained at all in de-escalation. Much like police officers need to have the power and authority to detain and arrest civilians, but many abuse that power and don't do anything to de-escalate, too many FAs turn minor disagreements into full fledged fights or diversions like this.
