Ask HN: Are Product Ripoffs by Large Companies Legal?

There is a lot of nuance to the subject, but there seems to be an obvious trend where large companies build a platform and then steal the ideas of smaller developers and incorporate it into the platform. It appears to my untrained eye to be anti-competitive and monopolistic.

A small for instance is Apple created Night Shift for IOS which is incredibly similar to F.lux which had been around for years ( but blocked from the AppStore).

Is this behavior legal? Does the HN community feel that it's ethical?