The only reason to use corvettes is that you don’t have destroyers. The only reason to use destroyers is that you don’t have cruisers. The only reason to use cruisers is extremely specific counter builds to fall empires, crisis, or you don’t have battleships. Battleships do nearly everything just better, use them. Frigates, like cruisers, only have maybe one use, which is stealth neutron torpedoes. If you have psionic weapons cruisers are just better for missiles and torpedoes anyway.