I think you're underestimating the TR set. TR is especially dangerous right now, with most teams relying on their fast, hard hitting offense teams to win. Mid to late game, Reuniclus can completely flip the match upside down and severely cripple or outright sweep an opposing offensive team. Calm Mind Reuniclus is quite outdated, and can't stand up to the offensive pressure in the current metagame, so TR is it's best bet. Despite it's lack of versatility right now, how strong Reuniclus is with Trick room is enough to keep it at B rank imo.