Personally I have a 2.19 recast which is around 0.07-0.08 seconds less than someone stacking something else. Which is approaching a 3-5% improvement in throughput and cast speed, which is not negligible. The problem is that people don't do the math on spell speed to figure out how much time you actually gain stacking it. I've already posted the numbers once but you can see them here http://forum.square-enix.com/ffxiv/t...83#post3658783
And again everyone playing this game has human error, delay to reaction, delay to reaching the correct movement location. This has nothing to do with stutter step casting or slide casting (though faster casts can be combined with slide casting). Spell speed fundamentally speeds up your casting this is completely independent of latency, server ticks or any of that. Regardless of how you choose to play your heals get to your targets faster.
You can certainly disagree that you don't feel the need to cast faster. But personally I don't see the other stats giving better gains right now. The gains on everything but Crit is terrible. And crit mostly just bloats overhealing unless you have shields.