Anything you can think of that's made of plastics was, prior to the mid 20th century, made of metal, ceramics, glass, fabric, or wood.

You'll realise these materials are usually much less suited to the task. In aggregate, the polymer industry was a huge benefit for humanity.

To take just one random example, I think electical wiring was insulated with fabrics in the early 20th century, which must have been expensive to make, and perhaps no too durable.

But really, plastics improved the manufacturability and performance of literally everything.