Thureophoroi aren't exactly weak. Of course you don't want them exposed to the real bad boys out there for a *very* long time; but you wouldn't want that with *any* unit regardless -- so how come you find them pitiful? Their main asset is that they're reasonably fast (faster than most infantry of their kind) and really don't tire all that easily. Fighting uphill you will see a noticeable difference compared with Thorakitai: indeed I have had Thorakitai routing before my Thureophoroi did, only because they had become exhausted so much earlier in the game.

But you have to keep in mind that they are meant as mobile troops -- not infantry of the line (their formation isn't thight enough.)