Honestly, while I'd love movement speed as much as the next guy (and my main jobs are BLM/SMN/RDM, so definitely ones that fall into this debate) I think it's meant to be more of an achievement. As far as I can see, the only jobs that get movement speed items easily are the ones that can use Hermes' Sandals, plus NIN and arguably BRD and SAM. On the other hand, the only job that can't boost movement speed by 12% or more through gear (as far as I can see) is DNC, which gets Chocobo Jig. The rest can use Herald's Gaiters, Crimson/Blood Cuisses, or Skadi's Jambeaux. Granted, not all of them want to, since THF/RNG can use Strider/Trotter Boots instead of Skadi, but you get the idea.

Which jobs that get easy movement speed (discounting ASA here, so I think this would be most easily defined as WAR/MNK/COR/PUP/BRD/SAM/NIN) have a decent combat use for it aside from escaping combat with the mob? WAR, MNK, and SAM have to be up close to deal decent damage most of the time, although Yoichinoyumi SAM is an exception. PUP could use the auto to achieve much of the same thing as movement speed boosts, albeit at the risk of losing your auto. BRD can't deal much damage anyway and NIN's ranged damage, from what I've seen, is pretty weak, which leaves COR. COR has ranged damage, and thus would get some use out of it, but it's also the least-played job in the game according to the last Census, so it probably needs the boost quite frankly.

Meanwhile, let's look at the jobs that have a harder time getting it, relying on Gaiters/WLegs/Skadi/Trotters. (Yeah, Trotter's is a bad example, but the only valid job on them for my argument is RNG.) First, Gaiters: WHM doesn't deal damage most of the time, but could use Gaiters to kite and cure simultaneously to an extent if for some reason that were ever, ever needed. BLM with gaiters is somewhat of a powerhouse, able to outrange most mobs with no trouble and then nuke them down. SMN doesn't get as much use out of them, since you could usually kite using Carby anyway, and most of your damage is from avatars. SCH, see BLM and WHM.

Next, WLegs: PLD/DRG/DRK don't really have a reason to be restricted to these and not Hermes', since none of them have significant ranged damage output. RDM could function like a BLM on these, perhaps to a slightly lesser extent due to lower nukes, while BLU using ranged spells would be pretty hard to deal with also. Lastly, Skadi/Trotter's: THF usually prefers to melee for damage, while BST would be using a bet and wouldn't need the movement speed. RNG, being primarily ranged damage, could probably get some real use out of these (shooting while kiting, methinks).

Yes, some of these arguments are fairly weak due to me only having a small amount of experience with some of the jobs involved. Sorry for that. Feel free to correct me where I'm incorrect or where there's a more valid point.

So, while extra unconditional movement speed would be nice to have, I believe the difficulty of obtaining it is fair given the amount of extra help it would be for quite a few of the jobs that have a harder time getting it.

(also, I love how COR is on three of the major sources of movement speed: Hermes', WLegs, and Skadi.)