Before getting all upset about, and drawing mostly negative conclusions from, the fact that the FISC rejects fewer than one in fifty warrant requests, it would be meaningful to ask how often other federal courts, and state courts, reject warrant applications. I would be quite surprised if the rate in other courts exceeded 2%. Warrant applicants know the requirements, the courts - all of them - know the requirements, and there are set procedures and forms used to ensure and verify that the requirements are met. Rejection of a warrant request is an outlier event.
The same is true of the presumed need to have a public representative before the FISC. It is not the norm for subjects of warrant requests to other courts to be represented by either personal or general counsel, despite that fact that a warrant to toss a residence or place of business is at least as invasive. It is the job of the court, as a formally independent branch of the government, to ensure that it issues warrants only on probable cause, based on sworn statements. The FISC is not different from other courts in this respect.
FISC proceedings are secret. So, in practical terms, are the warrant issue activities of other courts. The existence of a warrant normally becomes known when it is executed, and warrants are challenged, when they are, at execution time, by declining to perform the required action and appealing to a court for cancellation, or at trial, in motions to deny admissibility of any evidence their execution brought to light.