There's nothing hypocritical about the concept of a mob's size determining how well it can move.
You're right, there's nothing wrong with the concept, it's just not implemented well. Monster size is just a smaller factor that excaberates the larger one of generally poor pathing AI. I still think the other part (slowly building distance through obstructions that can at least logically hinder pathing temporarily) is a wash, though; if it's an obstacle, that means you have to run around it too, and if a monster of comparable size/movespeed takes any longer to get around it than you do, you're exploiting bad AI; no two ways about it.
One of the things I don't like about the entire discussion is the divorce of 'pinning' from 'kiting,' as pinning is simply taking kiting as present in FFXI to its logical conclusion. The only true kiting scenario is one in which you run forever in a straight, level line; if you deviate, you're starting to take advantage of the poor AI. In practice, even that scenario is impossible, as things as simple as a gradual incline in a path devoid of obstacles will cause the monster to deviate from its path. It's even possible (although difficult and rather pointless as stopping to cast breaks it) to pin a monster on a completely passable hill in certain places. There's probably a happy median somewhere in between, but as is, kiting primarily takes advantage of terrain, whether it's the Ix'MNK/DRK rooms in Sea, the numerous and awesome rock formations of Attohwa, or yes, that strangely epic fence in Ronfaure [S].
This is the primary reason why they will never ban people for, or otherwise disallow us from pinning; from a technical stanndpoint (and also from the standpoint that exploiting bad pathing AI is bad), it's the same damn thing that we've been doing since we figured out how to run away from sh*t intelligently. What are they going to do, ban us all retroactively? (I hope not!)
So, in other words, be careful what you wish for when you complain about bad pathing AI.
I find SE's comment to utilize terrain to our advantage as a bit of a farce, and I'm wondering if that was a translation liberty.
I was equally skeptical, so I just spammed GMs about it until they gave me an answer; GM showed up out of nowhere one day while I was killing a Krabkatoa, /waved, gave me the standard 'Good luck, Red Mage Lyltia" line, and peaced out. Was good enough for me.
As is, the only mobs I can think of where their environment is actually a factor in fighting them is Yovras and them being over water upping their regen rate. If we had more stuff like that with pros/cons for players/mobs alike, then I'd hold some more faith in the claim over putting environments to use.
I think Abyssea was kinda a step in that direction, with zone-wide systems you could influence like the Martello Cores, or Dominion making NMs more/less difficult based on the % of the lessers, etc., not to mention the Yellow/Blue proc rotations, all of which I think are pretty cool. Beyond that a lot of mobs since ToAU are affected by time/day/weather, which was also neat. I hope they take it further with whatever comes next.