Mantra of flames with perseverance?

The way I interpret it is that Onslaught is not a buff, but a property. However, there exist buffs out there, whose only property happens to be "You have Onslaught." So it is possible to gain onslaught and gain a buff for the duration of onslaught, but that still doesn't make Onslaught itself a buff. The buff is a container that doesn't do anything except grant the Onslaught property.

I'm open to being proved wrong, though!