Quote Originally Posted by Wigferth Ironwall
Hastatii really were more of a light infantry.
I disagree. The hastati fought in close combat on the front line, in close formation, with kit pretty similar to the principes and later legionnaires. I'd say they functioned as heavy infantry, even if they were not particularly well armoured.

I would reserve the term "light infantry" to refer to those who fought in loose formation - often skirmishing and fighting at range rather than moving to close quarters - the velites, peltasts, slingers, archers etc of the period.