My understanding is that the patent office checks if the patent is substantially similar to previous patents. A non-novel idea can easily get through if it is phrased in a different way or never appeared in an earlier patent.

I do not feel this is a problem. A patent just provides a legal presumption that you are allowed to file a lawsuit. Some people argue that this enables patent trolls, but patent trolls exist because con artists will always try to ride on the coattails of success. My view is that low standards for patentability provides protection against patent trolls: a company can patent early and often in the years before they hit it big and start attracting con men. Easy patentability also deepens the pool of well-documented prior art, providing more clubs with which to beat up patent trolls.