If heavy armor has no penalty, why would anybody produce or equip light armor?
Or are you supposed to start every class in light armor early game, then progress to medium, then to heavy?
If it is basically just "better armor" or "late game armor," what is the point of pretending that it is light, medium and heavy?
I'll try to explain, how would I see it. Any armor has its ... let's call it "energy core", which produces the energy, consumed by other armor suit systems. Heavy armor grants way better protection, can house some systems, which light armor can not (like backpack fabricator system or shoulder-mounted integrated weapons, for instance), but - it's augmentation system (aka power drive) consumes way more energy, than one of the light armor. This energy must be taken from other systems: shield generators, omni-tool, biotic amplifier etc. - which means (with the same energy core) weaker powers, or longer cooldowns, or weaker shields. Or - to keep all the stats on the same level - way more powerful (and less affordable) power core is needed.
I.e. the crucial moment is - "you cannot have all at once for certain cost": lighter suits propose higher mobility, stronger technical / biotic powers, shorter cooldowns, than medium and heavy ones of the same tier. While medium and heavy suits can afford to have less powerful shields (for they have armor in addition to them), or - should tolerate the lower mobility, or longer cooldowns for powers, than light suits of the same tier, but - support more powerful snap-in (aka connectable) and integrated weapons and grant way higher protection.
It's up to player, what to choose - according the the preferred playstyle.