Libyan Heavy Spearmen are trained veterans best used as a heavy shock infantry, with the lighter Libyan soldiers supporting.
It was an odd development that produced the Libyan Thorakitai. At virtually the same time, though at different places, both Carthage and the Greeks realized that a heavier version of the standard Thureophoroi would be a versatile and useful unit to have around. The most battle-hardened and loyal among the Libyan soldiers were gathered and re-equipped with heavier javelins and a mail shirt. This, combined with their veteran status makes them excellent soldiers, well able to stand up to any enemy. They are best used as a heavy shock infantry, with the lighter Libyan soldiers supporting.
Historically, the better Libyan warriors were given heavier armor by their commanders. They often fought with distinction alongside their more elite and more heavily armored compatriots, the elite African Infantry. They were a heavy infantry of wonderful quality, able to stand up to Romans and Greeks with ferocity and equal equipment.