Primal Primer in AMR is applied (or at least tracked) as a buff on the shaman that stacks when flametongue proc deals damage. In-game, it’s applied as a debuff on the target(s) that stacks when “melee attacks with flametongue active” deal damage - and that includes both melee attacks that proc flametongue (e.g. Stormstrike, autoattack, Lava Lash, Crash Lightning (on-use), etc.) and melee attacks that don’t (e.g. Sundering, Crash Lightning (on-SS/LL proc), Icy Edge, Hailstorm, etc.). Flametongue attack itself is not a “melee attack” historically and thus does not apply the Primal Primer debuff.
I took a look at some logs to verify this. You are right that it should be a debuff, but, it doesn’t behave exactly as you described.
The debuff is always applied by flametongue attack when it hits. It is also applied by Hailstorm, Sundering, Icy Edge, and Crash Lightning procs.
When you Stormstrike, each hit procs flametongue, and you apply a total of 2 stacks. When you cast Crash Lightning, each hit procs flametongue and applies one stack per hit of flametongue. When you Stormstrike with Crash Lightning up, the crash lightning proc does add one stack to each target. Sundering also applies one stack.
Auto Attacks themselves don’t actually apply a stack of the debuff, although you could probably say that autos proc it and flametongue doesn’t. The combat logs make it seem like it is the flametongue attack itself proc’ing the debuff, though.
Thanks for the heads up, I’ll make an update and re-rank the power.