Useless? I fail to see why. The election would be over before this issue is resolved on its merits. if any.
I'll help the others see what you refuse to acknowledge.
The legality of Cruz's name being on the ballot is a state law issue. Your argument was that federal courts would not reach the merits, and would instead dismiss the suits on procedural grounds, such as ripeness, judiciability, or some other rationale that resembles those. Being dismissed in federal courts, while an interesting academic exercise, does not resolve how state courts might rule, nor does it address the existence (or not) of state laws that bear on putting the names of ineligible candidates on the state ballots.
In short, the argument is on whether a case lies in any court, which is state court in the first place, and your response is that no case lies in a federal court.