Rage of Halone does apply it's enmity increase regardless of Combo, but it's 160 attack potency lower to that increase Enmity modifier means much less. The enmity increase on ability that do that is an increase multiplier of the normal enmity generated by an attack of that damage. Keeping in mind that i do not know the exact mutipliers it works kind of like this. (this is purley an example and not real numbers)

Attack dealing 100 damage = 100 enmity
Rage of Halone out of combo deals 100 damage = 300 enmity
Rage of Halon in combo deals 260 damage = 780 enmity

Again I have no idea what the actual numbers look like, but that's the basic premise. Shield oath also adds an enmity multiplier combo once you learn it.

As for snatching threat at the beginning of a pull on a single target I would suggest Shield lob followed by your combo. Flash does blind them which is notable for minor damage mitigation and some threat generation, but your combo is better.