This is a distraction from the problem, they are courts because they function as courts in providing binding precedent on how laws are interpreted. The people making the decision (FISA judges) are Article III federal judges (i.e. nominated by the President, confirmed by Senate), picked by SCOTUS Chief Justice, and continuously vetted for security clearance by exec branch. Public interest importance of their decisions are supposed to be released (for legislators to be able to preform their legislative function) within 180 days.
That is the problem -- if legislators aren't informed how the laws they wrote are interpreted / used by the executive, they cannot reason about how to legislate next.
That is the problem -- if legislators aren't informed how the laws they wrote are interpreted / used by the executive, they cannot reason about how to legislate next.