\'soft\' eastern soldiers

[D B Campbell]

Do you know of any specific (modern) literature that states this.

You need: Everett Wheeler, "The laxity of the Syrian legions", in: David Kennedy (ed.), The Roman Army in the East (Journal of Roman Archaeology, Suppl. 18. Ann Arbor, 1996), pp. 229-276. (Reviewed here.)

It's a theme that Wheeler often comes back to (e.g., in a 2010 volume, he writes: "the laxity of Syrian legions was a topos reflecting Latin authors' prejudices about the supposed enervating effects of life in the sensuous and luxurious East. ... As demonstrated in 1996, the topos of the laxity of Syrian legions has no basis in fact. Syrian and eastern legions in general were as militarily efficient as those on other frontiers."

Edit: You weren't wrong, David!