The best ground on which the defendant ( Company S ) can dismiss the suit filed by the plaintiff (Company T) is the standing to sue.
What is standing to sue?
Standing to sue refers to a situation where the plaintiff who has filed the case must prove with appropriate proof of having damages or injuries in respect of the conduct of the defendant.
In the provided case, Company T has to prove that the products of Company S are actually defective through appropriate evidence. If Company T can't able to prove their alleged claim before the court, then the case is decided in the favor of the defendant party, that is, Company S.
Therefore, the standing to sue can be used as a ground by Company S for dismissing the claim of Company T.
Learn more about the standing to sue in the related link: