Long Press power while pressing volume down works on all Android devices I've used to date.
And that's ignoring the fact that disconnecting power, waiting a few days and then reconnecting it will inevitably let you cold boot it, too (which this would be an equivalent to - as far as I understood it)
Your are absolutely correct. I mixed it up from playing with various Android versions in 2010-2016. The long press alone got the reboot, and the volume down + power booted into the bootloader. Hence my memory with both, as I always pressed both until the bootloader was available - but you are right, long press power is enough for hard off
