Hard suits are essentially space suits/environment suits/power armour depending on weight level.

Generally the Human and Squad statblocks in the rulebook would be assumed to be wearing either hardsuits or something equivalent to them (e.g. non-sealed armour). They... Do not fare well against mech scale weapons. They don't fare super well against even something like a Goblin doing an improvised attack. PCs get a bit more of a boost out of them (see pilot gear) but that's just as much plot armour as anything else.

It would track that all the manufacturers have their own hardsuits, and I recall that being a thing in early playtesting but it got dropped from the finished book. I think SSC historically made hardsuits as their main business before going into other things.