Emet-Selch, The Brother Hypothesis

[Iscah]

I [Garleans] are all Tall Humans, as base Garleans are Human Heads on Elezen Bodies at Max Sliders. With named Garleans all being buff Roegadyn Sized Humans.

Human heads on Elezen bodies, sure. (Though some are Hyuran instead.) But they're not necessarily max sliders at all – they can still be set to whatever height they want the model to be. As I linked earlier, Emet's model is set at zero height.

And by "all named Garleans" I think you mean Zenos and Varis, because plenty of the Elezen- and Hyuran-sized ones have names.