This summary is not the rule. The rule text controls.
If you're asking a court for a writ of certiorari, having another legal option available doesn't stop the court from granting it. In other words, the judge can't refuse your request for this type of relief just because you had some other way to fight the problem, like an appeal or a different lawsuit.
However, this type of relief has real limits. When a court reviews your case under certiorari, it can only look at two things: whether the lower court or agency had the legal authority (jurisdiction) to act, and whether what they did was legal. The court won't re-examine the facts of your case or decide if the outcome was fair. It's a narrow check on power and legality, not a full do-over.
This means certiorari is a specific tool for a specific problem. If you believe a judge, board, or agency acted outside their authority or broke the law in how they handled something, this rule allows you to challenge that, even if you technically had another path available. But don't expect the court to revisit every detail of the case. Unless a specific law says otherwise, the review stays focused on those legal and jurisdictional questions.