Tanks always have a harder climb in the rankings, regardless of which tank it is. Although, there were quite a few War's in the top 100 on Primal last season, if I recall correctly. Regardless, it's not that War is "easy" per se. It just has less demands on their attention in comparison to Pld.
When you play as War, you're basically focused purely on offensive support. You have a rotation, one party defense CD (two if you count Mythril Tempest ... on that obnoxiously long CD), and that's pretty much it. Pld, by comparison, has to constantly flip flop around between offensive support and defensive support. They have to manage stuns, be aware of bursts on both teams, keep count of CC resist timers, and manage 3 defensive CD's as well as supplementary healing with Clemency. At any given moment, Pld's have to be totally aware of the exact status of both teams (healing, hp bars, burst timers, and CC resist timers) and make a judgement call on where they can be of the best use. The weight of those judgments are heavier, as well, because their diverse utility means that they will be leaving a deficiency somewhere on the team each time they choose to be someplace else. That doesn't make War "easy," mind you. It just makes it different. On a rotation point of view, War is technically harder.
