Looking back, I'm pretty sure that the exact wording was that Pld is the hardest tank for maintaining threat, specifically, due to the fact that they have the lowest enmity multiplier of all three tanks. I'm not sure why you would even contest this, considering it is a well documented fact. The numbers have been outed a long time ago. Throw a stone into the Tank forums and you'll find them somewhere, because it's been discussed a dozen times over. If you have ever read anything about Pld's or used them at all in the past then this is something that you should know very well. Further, if you main-ed Pld in the past, then you should also know that Pld's optimize their Dps when rotating RoH across several targets to keep hate, instead of using Flash which deals 0 Dmg. This is Pld Mob tanking 101, typically something Pld's learn before they get Shield Oath.
After HW, Pld's got 2 new combos that are by far harder to work into their rotation when MOB tanking, specifically, without losing enmity. The new Pld optimization for mob tanking would see the Pld rotating RoH to maintain threat across as many targets as possible before switching to GB or RA to maximize their Dps. Ideally, to maintain maximum Dps, the Pld should be avoiding additional uses of Flash as much as possible since Flash deals 0 dps. Again, this is due to the fact that they have a well documented and substantially lower enmity multiplier than War's and Drk's. That's not a big secret here.
Now, does that mean that it is overly "hard?" No. You're right to say that any Pld tanking at end-game content should be able to hold enmity no problem. However, do Pld's have a harder time maintaining threat on multiple targets while optimizing their Dps using GB and RA and without resorting to additional Flash spams (which are not optimal due to the fact that Flash does 0 dps)? Most certainly. This is not even a question, and I don't know why anyone would ever say otherwise, given that the numbers have been worked out so often it's sickening that SE hasn't said anything about it. By comparison, War's and Drk's have far more freedom to do practically whatever they want during a mob pull and still hold enmity with the minimum effort.