Spiky is not necessarily random. Spiky means exactly what it implies; there are large spikes in the chart when looking at the data over a period of time.
(Besides in math nothing is truly random, there is always a pattern)
It's not about the "long run". It is about where the hate levels currently are based on the hundred odd factors taking place during an encounter.
Once again, in eight mans. Every single time I try to do the normal Paladin tanking rotation described in http://forum.square-enix.com/ffxiv/threads/122272-Guide-Paladin-Tanking-Compendium-2.0.1 I cannot maintain threat on the mob.
Every. Single. Time.
The only thing that gains and maintains threat for me is spamming Halone.
Doing the combo gives opportunities to lose threat, meaning the mob takes off to go attack DPS / healer. Hard to generate aggro on an enemy running away from you when all you have is Provoke's +1 enmity bonus, and Shield lob on a cooldown.
Yeah, it is probably because my gear is 20-30 item levels below everyone else. But that won't change unless I can keep the boss on me, there is no other way to gear up. Even if I wanted to buy HQ crafted gear I would still need to buy crafting items with tomes and sell them on the AH house to make enough cash to buy said gear.
So I do what I can to keep aggro and do the runs, as does any other tank in my situation. And it's not fun. I am sure it is a contributing factor to why there aren't as many tanks.
And its a simple thing for SE to fix, and will result in more people playing tanks.