First of all, Shedinja's evolutionary line is based off of a cicada. Cicadas are very loud bugs due to drums located in their wings that spend most of their lives underground in the nymph stage, feeding around the roots of trees. To enter their next stage of life, they must shed their skins on a nearby surface, leaving behind an empty brown shell. They are typically seen emerging from the backs of these shells, which explains the hole in its back. When cicadas leave their shells as adults, they don't do anything with it, just leaving it where it was, which explains why you get a Shedinja AND a Ninjask after evolving with space in your party. It also explains why Shedinja has little to no health, as the cicada shell has no creature inside it. Essentially Shedinja is an enchanted cicada shell, but without a life essence it doesn't have much health.
Shedinja isn't weak if you give it a place to shine. Building a team around Shedinja would actually be a great opportunity to try new strategies because its low HP makes an interesting challenge. Teammates such as Cradily can stall out and take down pesky Fire and Flying types, but its slow Speed may grant the opponent a turn, especially threats like Talonflame and Charizard. It can also use its Grass typing to an advantage against Rock types.
However, a faster teammate is necessary and other options could include Mega Gallade with Night Slash in its moveset depending on how slow the opponent is-- if it can outspeed the Ghost type fighting it, then it can land a blow to a possible threat with a Dark type move. It also is part Fighting and Psychic, giving it wide access to moves that could hinder previously mentioned Dark types.
Those are just a few options though, and there are plenty better ones. And you still need to be careful with Shedinja. It's very fragile, so don't get reckless with your strategy. You cannot afford even one point of damage or a spot on your team will be jeopardized.
