Very misleading statistic and I don't think you thought this through. Search warrant applications in general are almost never denied, precisely because those seeking the warrant don't submit marginal applications. If an application is insufficient judges usually do not deny them, they return them to the prosecutors/agency demanding further evidence or clarification.
The question you should be asking yourself is how FISA compares to regular courts, and if anything it appears FISA is TOUGHER than them. From 2006 through 2016 federal courts fielded 32,090 intercept requests and rejected only 9.
http://www.uscourts.gov/statistics/table/wire-7/wiretap/2016/12/31
Are you now claiming that the entire US federal court system is somehow illegitimate?